**Introduction to Scientific Discipline Agrophysics — History and Research Objects**

B. Dobrzański, S. Grundas and A. Stępniewski

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/56982

## **1. Introduction**

### **1.1. Agrophysics's definition and scope**

From the very beginning of its existence the definition of Agrophysics as a science was described a number of times. In general, Agrophysics is a branch of natural and agricultural sciences which applies physics into agriculture. Therefore sometimes it is also called agricul‐ tural physics. It explores agricultural materials and processes to describe their physical properties in order to assure best quality of agricultural products or raw material for industry, taking into account the role of environment and other factors. As a field of science, Agrophysics is of interdisciplinary scope and it is closely related to Biophysics. It is however limited strictly to the agricultural environment, i.e., soil, plants and animals and also takes into account the knowledge of Agronomy and Agriculture Engineering.

Agrophysics deals with physical processes in the soil-plant-atmosphere system, taking into account various external factors (climate, impact of the machinery, pollution) and issues related to the growth, harvest, transport, storage and processing of agricultural materials.

Some examples of the wide scope of agrophysical investigation are: developing systems for monitoring and controlling the condition of soil (moisture, salinity etc.) and plant growth (maturity), evaluation of the soil's susceptibility to water and wind erosion, moni‐ toring and diagnosis of soil biological activity, determination of pollution in agricultural products (fruits, vegetables etc.), the assessment of the technological value of grain, evalu‐ ation of quality of fruits and vegetables during their storage and changes of their nutri‐ tion value during storage.

© 2013 Dobrzański et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Dobrzański et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

physics to agriculture. Most attention was given to soil physics, e.g., he studied water-holding capacities, moisture requirements of plants, aeration, movement of water in soils, movement of groundwater, and the drafts of plows. During his last years in Madison he also began studies

Introduction to Scientific Discipline Agrophysics — History and Research Objects

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5

**•** The soil: Its nature, relations and fundamental principles of management. Macmillan, 1895.

F.H. King's observations and investigations could be nowadays regarded as a contribution to the so called sustainable agriculture. He died in 1911 in Madison, Wisconsin and his last two

Beginnings of application of physics in agriculture in Europe were in Soviet Russia. Agro‐ physical research was commenced in Russia in the middle of XX century. Russian physicist Abram Fieodorovich Ioffe (1880–1960) is regarded as the initiator of this branch of science. He studied measuring methods and used them in agriculture, biology and agrochemistry. He studied electromagnetism, radiology, crystals, high-impact physics, thermoelectricity and photoelectricity. He established research laboratories for radioactivity, superconductivity, and nuclear physics. In 1932 Ioffe organized the Institute of Physics and Agriculture in Leningrad (Sankt Petersburg at present) and became its first director. A.F. Ioffe published two funda‐ mental works entitled: Physics and Agriculture (1955), and Physics for Agriculture (1959). His successors included: A.F. Chudnovsky (1910–1985), F.E. Koliasev (1898–1958);P.V. Vershinin (1909–1978); I.B. Revut (1909–1978), S.V. Nerpin (1915–1993), E.I. Ermakov (1929–2006), N.F. Bondarenko's (1928– 2003); I.S. Lisker; A.M. Globus, V.P. Yakushev and others. The research topics undertaken by the above mentioned scientists were: mathematical modeling of agri‐ cultural production, simulation of agrophysical systems and processes; interaction of biolog‐ ical objects with different physical fields (light, gravity, magnetic, electromagnetic, acoustic, electrostatic), information technologies of production management in arable farming and plant growing, agrophysical instrumentation, elaboration of vegetative systems in controlled climate, a new type of coordinate precision agriculture as the first step to the creation of the

The second scientific Institute whose main field of research is Agrophysics was established in Lublin, Poland. Created in 1968 by prof. Bohdan Dobrzański, the Institute of Agrophysics of the Polish Academy of Sciences was soon recognized as a leading research centre not only in

of soil fertility. He has been called the "father" of soil physics in the USA.

King published some books, the titles of which prove his scientific interest:

**•** Irrigation and drainage. Macmillan, 1898. New York.

**•** Physics of agriculture. F.H. King, 1901. Madison, WI.

**•** Soil management. Orange-Judd, 1914. New York.

books were completed and published after his death.

**•** Farmers of forty centuries. F.H. King, 1911. Madison, WI.

New York.

"electronic farmer".

**•** Elementary lessons in physics of agriculture. F.H. King, 1894. Madison, WI.

**•** Ventilation for dwellings, rural schools and stables. F.H. King, 1908. Madison, WI

**Figure 1.** Graphical description of the definition of Agrophysics

The following definition of Agrophysics was recently included in the "Encyclopedia of Agrophysics":

"Agrophysics is a science that studies physical processes and properties affecting plant production. The fundaments (nutrients) and energy (light, heat) transport in the soil– plant–atmosphere and soil–plant–machine–agricultural products–foods continuums and way of their regulation to reach biomass of high quantity and quality with the sustainability to the environment. The knowledge of physical phenomena in agricultural environment allows increasing efficiency of use of water and chemicals in agriculture and decreasing biomass losses during harvest, transport, storage, and processing."

Agrophysics therefore aims at ecological use of agricultural ecosystem to assure best quality of agriculture products and the preservation of agricultural landscapes.

### **2. History**

In the end of XIX century scientists recognized the need of application of physics to agriculture. The pioneer in this field of research was probably Franklin Hiram King. He was born in 1848 in Whitewater Wisconsin USA. He graduated from Cornell University and served as professor of natural sciences at River Falls State Normal School and after that as professor of agricultural physics at the University of Wisconsin. In 1888 the University of Wisconsin called him to the Chair of Agricultural Physics, the first of its kind in America. F.H. King was interested in a wide range of scientific problems but he made his major contributions to the applications of physics to agriculture. Most attention was given to soil physics, e.g., he studied water-holding capacities, moisture requirements of plants, aeration, movement of water in soils, movement of groundwater, and the drafts of plows. During his last years in Madison he also began studies of soil fertility. He has been called the "father" of soil physics in the USA.

King published some books, the titles of which prove his scientific interest:


**Figure 1.** Graphical description of the definition of Agrophysics

Agrophysics":

4 Advances in Agrophysical Research

and processing."

**2. History**

The following definition of Agrophysics was recently included in the "Encyclopedia of

"Agrophysics is a science that studies physical processes and properties affecting plant production. The fundaments

(nutrients) and energy (light, heat) transport in the soil– plant–atmosphere and soil–plant–machine–agricultural

products–foods continuums and way of their regulation to reach biomass of high quantity and quality with the

sustainability to the environment. The knowledge of physical phenomena in agricultural environment allows increasing

efficiency of use of water and chemicals in agriculture and decreasing biomass losses during harvest, transport, storage,

Agrophysics therefore aims at ecological use of agricultural ecosystem to assure best quality

In the end of XIX century scientists recognized the need of application of physics to agriculture. The pioneer in this field of research was probably Franklin Hiram King. He was born in 1848 in Whitewater Wisconsin USA. He graduated from Cornell University and served as professor of natural sciences at River Falls State Normal School and after that as professor of agricultural physics at the University of Wisconsin. In 1888 the University of Wisconsin called him to the Chair of Agricultural Physics, the first of its kind in America. F.H. King was interested in a wide range of scientific problems but he made his major contributions to the applications of

of agriculture products and the preservation of agricultural landscapes.

F.H. King's observations and investigations could be nowadays regarded as a contribution to the so called sustainable agriculture. He died in 1911 in Madison, Wisconsin and his last two books were completed and published after his death.

Beginnings of application of physics in agriculture in Europe were in Soviet Russia. Agro‐ physical research was commenced in Russia in the middle of XX century. Russian physicist Abram Fieodorovich Ioffe (1880–1960) is regarded as the initiator of this branch of science. He studied measuring methods and used them in agriculture, biology and agrochemistry. He studied electromagnetism, radiology, crystals, high-impact physics, thermoelectricity and photoelectricity. He established research laboratories for radioactivity, superconductivity, and nuclear physics. In 1932 Ioffe organized the Institute of Physics and Agriculture in Leningrad (Sankt Petersburg at present) and became its first director. A.F. Ioffe published two funda‐ mental works entitled: Physics and Agriculture (1955), and Physics for Agriculture (1959). His successors included: A.F. Chudnovsky (1910–1985), F.E. Koliasev (1898–1958);P.V. Vershinin (1909–1978); I.B. Revut (1909–1978), S.V. Nerpin (1915–1993), E.I. Ermakov (1929–2006), N.F. Bondarenko's (1928– 2003); I.S. Lisker; A.M. Globus, V.P. Yakushev and others. The research topics undertaken by the above mentioned scientists were: mathematical modeling of agri‐ cultural production, simulation of agrophysical systems and processes; interaction of biolog‐ ical objects with different physical fields (light, gravity, magnetic, electromagnetic, acoustic, electrostatic), information technologies of production management in arable farming and plant growing, agrophysical instrumentation, elaboration of vegetative systems in controlled climate, a new type of coordinate precision agriculture as the first step to the creation of the "electronic farmer".

The second scientific Institute whose main field of research is Agrophysics was established in Lublin, Poland. Created in 1968 by prof. Bohdan Dobrzański, the Institute of Agrophysics of the Polish Academy of Sciences was soon recognized as a leading research centre not only in Eastern and Central Europe, but also in the global research. Numerous professors and younger researchers from the Institute frequently visited leading universities from Western Europe, Japan and the USA, bringing home the knowledge of recent trends and novel methods in the research field. In turn, the high quality of IA staff attracted a number of doctoral students and young researchers from Poland and abroad.This attractiveness, especially to young research‐ ers made the Institute become also a leading educational centre at an advanced level in numerous research areas connected with environment, agriculture and food sector. The results of the research activities undertaken in the Institute were introduced into industry and gave basis for new products and technologies. The outstanding scientists of that period were: I. Dechnik (1929 - 2003), R. Walczak (1943 - 2003), M. Malicki (1939 - 2009), J. Stawiński (1942 - 2005), B. Szot (1933 – 2012), J. Gliński, W. Stępniewski, J. Lipiec, K. Konstankiewicz,

At present, there are more than 100 employees of interdisciplinary character. The scientific staff of the institute constitutes an interdisciplinary team of physicists, chemists, agronomists,

Introduction to Scientific Discipline Agrophysics — History and Research Objects

http://dx.doi.org/10.5772/56982

7

Agrophysics initially focused mainly on the study of soil and plant materials. Over time, this research area started to gradually expand, on the one hand including ever more elements of the soil-plant-atmosphere system, on the other hand, more and more focused on the process of food production and its quality - from the stage of agricultural production through the

Agrophysics began also to be useful in the wider environment, being a part in the study of not only the degradation of soils, but also researching marshy land formation and greenhouse gas emissions. Currently Agrophysics concentrates on a number of agricultural specialties, it is used to interpret interactions, design, control and optimization of processes. It is also widely used in environmental protection, pedology, tillage and plant engineering, agriculture, agri-

Agrophysics was developed also in other countries, initially in Eastern European countries. In Czechoslovakia (Prague) R. Řezniček together with his coworkers (J. Blahovec, J. Pecen, P. Hnilica) conducted some important investigations at the Chair of Physics of Prague Agricul‐ tural University. They concentrated on physical properties of cereal grains and developed some interesting testing methods. In Czech M. Kutilek from Czech Technical University in Prague conducted advanced studies within soil science too. Also in Hungary (Gödöllö and Budapest) researchers carried out studies on physical properties of agricultural materials: soil, seed, grains, vegetables and fruits. In this context the following names should be mentioned: G. Sitkei, I. Husar, G. Várallyay, I. Farkas and others. Also German researchers joined inter‐ national agrophysical society. The universities in Hohenheim (H-D. Kutzbach, E. Schlihting, K. Stahr), Bonn (K.-H Kromer), Kiel (R. Horn), Berlin (G. Wessolek) and in Potsdam (J. Helebrand) were engaged in application of physics in agriculture. The events called "Agrofizik Tagung" were organized on a regular base in Germany. These symposiums gathered scientists interested in this topic from Germany. Agrophysics was researched also in Spain. Spanish scientists were interested both in soil (J. Moreno, M. Aranda and D. de la Rosa) and fruit properties (M. Ruiz-Altisant, J. Caniavate). Belgium has also undertaken serious research activities to become a strong agrophysical centre. Catholic University in Louvain (J. DeBaer‐ demaker, B. Nicolai) and University of Ghent (M. De Boodt, D. Gabriëls) were main centers of agrophysical research there. In France agrophysics was developed in INRA Montfavet (S. Auber, P. Varoquaux), while in Italy the University of Torino (A. Ferero) was the centre of agrophysical studies. Same investigation were also conducted in Belarus and a leader there was I.I. Lishtvan. In Austria prof. W.E.H. Blum interested in some agrophysical aspects of soil

period of storage of agricultural products, their processing until the final product.

horticulturists, biologists, engineers, geographers and mathematicians.

food technology, and others.

**3. Agrophysics in other countries**

sceinces. From Sovakia it is necessarry to mentione Jech.

**Figure 2.** Coworkers of prof. B. Dobrzański from the Instite of Agrophysics at the Conference in Prague 1985 (from left; in the front row: R. Walczak, B. Szot, G. Skubisz, B. Dobrzański, J. Gliński; in the secondrow: M.Molenda, A. Pukos, W. Stępniewski, W. Woźniak, A. Kuczyński, K. Konstankiewicz, J. Lipiec)

The main fields of scientific activity of the Institute of Agrophysics PAS were as follows: investigation of physical and physical–chemical processes of mass and energy exchange in the soil – plant – atmosphere system, physical properties of agricultural materials and processes affecting plant production as well as processes related to gathering, transport and storage of agricultural materials.

The main feature of these studies was the elaboration of new theoretical and experimental research methods, developing of physical – mathematical models and their experimental verification, processing of data, taking into account their variabilityin time and space. Data bases and thematic maps created in this process can be used in practice for agricultural and environmental protection.

At present, there are more than 100 employees of interdisciplinary character. The scientific staff of the institute constitutes an interdisciplinary team of physicists, chemists, agronomists, horticulturists, biologists, engineers, geographers and mathematicians.

Agrophysics initially focused mainly on the study of soil and plant materials. Over time, this research area started to gradually expand, on the one hand including ever more elements of the soil-plant-atmosphere system, on the other hand, more and more focused on the process of food production and its quality - from the stage of agricultural production through the period of storage of agricultural products, their processing until the final product.

Agrophysics began also to be useful in the wider environment, being a part in the study of not only the degradation of soils, but also researching marshy land formation and greenhouse gas emissions. Currently Agrophysics concentrates on a number of agricultural specialties, it is used to interpret interactions, design, control and optimization of processes. It is also widely used in environmental protection, pedology, tillage and plant engineering, agriculture, agrifood technology, and others.

## **3. Agrophysics in other countries**

Eastern and Central Europe, but also in the global research. Numerous professors and younger researchers from the Institute frequently visited leading universities from Western Europe, Japan and the USA, bringing home the knowledge of recent trends and novel methods in the research field. In turn, the high quality of IA staff attracted a number of doctoral students and young researchers from Poland and abroad.This attractiveness, especially to young research‐ ers made the Institute become also a leading educational centre at an advanced level in numerous research areas connected with environment, agriculture and food sector. The results of the research activities undertaken in the Institute were introduced into industry and gave basis for new products and technologies. The outstanding scientists of that period were: I. Dechnik (1929 - 2003), R. Walczak (1943 - 2003), M. Malicki (1939 - 2009), J. Stawiński (1942 -

2005), B. Szot (1933 – 2012), J. Gliński, W. Stępniewski, J. Lipiec, K. Konstankiewicz,

**Figure 2.** Coworkers of prof. B. Dobrzański from the Instite of Agrophysics at the Conference in Prague 1985 (from left; in the front row: R. Walczak, B. Szot, G. Skubisz, B. Dobrzański, J. Gliński; in the secondrow: M.Molenda, A. Pukos,

The main fields of scientific activity of the Institute of Agrophysics PAS were as follows: investigation of physical and physical–chemical processes of mass and energy exchange in the soil – plant – atmosphere system, physical properties of agricultural materials and processes affecting plant production as well as processes related to gathering, transport and storage of

The main feature of these studies was the elaboration of new theoretical and experimental research methods, developing of physical – mathematical models and their experimental verification, processing of data, taking into account their variabilityin time and space. Data bases and thematic maps created in this process can be used in practice for agricultural and

W. Stępniewski, W. Woźniak, A. Kuczyński, K. Konstankiewicz, J. Lipiec)

agricultural materials.

6 Advances in Agrophysical Research

environmental protection.

Agrophysics was developed also in other countries, initially in Eastern European countries. In Czechoslovakia (Prague) R. Řezniček together with his coworkers (J. Blahovec, J. Pecen, P. Hnilica) conducted some important investigations at the Chair of Physics of Prague Agricul‐ tural University. They concentrated on physical properties of cereal grains and developed some interesting testing methods. In Czech M. Kutilek from Czech Technical University in Prague conducted advanced studies within soil science too. Also in Hungary (Gödöllö and Budapest) researchers carried out studies on physical properties of agricultural materials: soil, seed, grains, vegetables and fruits. In this context the following names should be mentioned: G. Sitkei, I. Husar, G. Várallyay, I. Farkas and others. Also German researchers joined inter‐ national agrophysical society. The universities in Hohenheim (H-D. Kutzbach, E. Schlihting, K. Stahr), Bonn (K.-H Kromer), Kiel (R. Horn), Berlin (G. Wessolek) and in Potsdam (J. Helebrand) were engaged in application of physics in agriculture. The events called "Agrofizik Tagung" were organized on a regular base in Germany. These symposiums gathered scientists interested in this topic from Germany. Agrophysics was researched also in Spain. Spanish scientists were interested both in soil (J. Moreno, M. Aranda and D. de la Rosa) and fruit properties (M. Ruiz-Altisant, J. Caniavate). Belgium has also undertaken serious research activities to become a strong agrophysical centre. Catholic University in Louvain (J. DeBaer‐ demaker, B. Nicolai) and University of Ghent (M. De Boodt, D. Gabriëls) were main centers of agrophysical research there. In France agrophysics was developed in INRA Montfavet (S. Auber, P. Varoquaux), while in Italy the University of Torino (A. Ferero) was the centre of agrophysical studies. Same investigation were also conducted in Belarus and a leader there was I.I. Lishtvan. In Austria prof. W.E.H. Blum interested in some agrophysical aspects of soil sceinces. From Sovakia it is necessarry to mentione Jech.

Agrophysics was developed not only in Europe. A fundamental publication on this topic "Physical Properties of Agricultural Products" has been written by N.N. Mohsenin – scientist of Iranian origin who worked in the USA. Prof. A. Tabatabaeefar is a continuator of Mohsenin agrophysical research in Iran. There were also other scientists interested in agricultural physics i.e. S. Gunasekaran, O.R. Kunze, J.I. Ross, G. Brusevitz, F. McClure, Y.A. Pachepsky, S.A. Thompson, P.P. Chen and others. Some topics of applied physics in agriculture were under‐ taken in Japan (R. Hatano) and China (T. Ren,).

A number of scientific papers that were submitted and presented during the above mentioned conferences were published both in conference materials as well as in special issues of scientific

Introduction to Scientific Discipline Agrophysics — History and Research Objects

http://dx.doi.org/10.5772/56982

9

Institute of Agrophysic of the Polish Academy of Sciences is also the publisher of an outstand‐ ing scientific journal entitled "**International Agrophysics**". The editorial board states that: "the journal focuses on physical properties and processes affecting biomass production and processing. The main topics are: mass (water, air, plant nutrients) and energy (light, heat) transport in the soil-plant-atmosphere continuum, ways of their regulation in order to reach biomass of high quantity and quality. The description of new methods and devices for measurements of the physical properties of agro- and biomaterials are published. The journal is also open to wider aspects of environmental and agricultural physics". The present Editor-

International Agrophysics is indexed by Journal Citation Reports with 1,574 impact factor.

A second journal published by the Institute of Agrophysics is "Acta Agrophysica". Acta Agrophysica has been published since 1993. At the beginning it contained mainly monogra‐ phies and dissertations which were published irregularly. From 2012 Acta Agrophysica is a quarterly. It publishes papers presenting the results of fundamental and applied studies from the field of application of physics for the solution of problems relating to the management and protection of the natural environment, sustainable agriculture, and food processing. Papers can be published both in Polish and English. The present Editor-in-Chief is prof. J. Horabik.

The third journal published by the Institute of Agrophysics is "Acta Agrophysica Monogra‐ phiae" which publishes reviewed papers based on original research results as well as mono‐ graphs pertaining to the field of agrophysics. The monographs are published in Polish or

In order to facilitate international collaboration and allow unification of terminology, a number of bilingual and multilingual dictionary of agrophysical terms (nomenclature) was prepared under editorial supervision of prof. Ryszard Dębicki and prof. Jan Gliński. The following

"Atlas of the Redox Properties of Arable Soils in Poland" prepared by Ostrowski, J.; Stęp‐ niewska, Z.; Stępniewski, W.; Gliński, J. was published 1996. It contains a wide range of data on soils in Poland presented in the form of cartographic maps. The Atlas gives a comprehensive

languages were taken into consideration: English, Russian, French, Spanish, German.

The above mentioned journals are available in electronic versions on the internet.

English. The present Editor-in-Chief is prof. J. Horabik.

**6. Dictionaries and books, maps**

journals.

**5. Agrophysical journals**

in-Chief is prof. J. Gliński.

In Canada at the Guelph University physics in agriculture was practiced by number of researchers (W.K. Bilanski, R.L. Kushwaha). Also at University of Saskatchewan F. Sosulski. Agrophysics was developed even in New Zealand by C.J. Studman.

In Israel some aspects of agrophysics were studied by I. Shmulevich, E. Bresler, K. Peleg.

The above mentioned names and centres do not exhaust the list of places and persons who conduct their investigations in the field of applied physics in agriculture. These are only examples of people who cooperated with scientists from the Institute of Agrophysics PAS proving that agrophysics is a world-wide recognized science discipline.

## **4. Agrophysical conferences**

Conferences on Agrophysics have always been an occasion for long discussionson all aspects of physical, physicochemical and biological processes of mass and energy exchange in soilplant-atmosphere system and of plant production, as well as characteristics of agricultural products and materials, agrophysical measuring methods, soil degradation and remediation problems.

Since Agrophysics became a widely practiced discipline of science there were already a number of agrophysical conferences organized. They gathered scientists which main research interests focus on physics in agriculture. The conferences were organized as follows:


A number of scientific papers that were submitted and presented during the above mentioned conferences were published both in conference materials as well as in special issues of scientific journals.

## **5. Agrophysical journals**

Agrophysics was developed not only in Europe. A fundamental publication on this topic "Physical Properties of Agricultural Products" has been written by N.N. Mohsenin – scientist of Iranian origin who worked in the USA. Prof. A. Tabatabaeefar is a continuator of Mohsenin agrophysical research in Iran. There were also other scientists interested in agricultural physics i.e. S. Gunasekaran, O.R. Kunze, J.I. Ross, G. Brusevitz, F. McClure, Y.A. Pachepsky, S.A. Thompson, P.P. Chen and others. Some topics of applied physics in agriculture were under‐

In Canada at the Guelph University physics in agriculture was practiced by number of researchers (W.K. Bilanski, R.L. Kushwaha). Also at University of Saskatchewan F. Sosulski.

In Israel some aspects of agrophysics were studied by I. Shmulevich, E. Bresler, K. Peleg.

The above mentioned names and centres do not exhaust the list of places and persons who conduct their investigations in the field of applied physics in agriculture. These are only examples of people who cooperated with scientists from the Institute of Agrophysics PAS

Conferences on Agrophysics have always been an occasion for long discussionson all aspects of physical, physicochemical and biological processes of mass and energy exchange in soilplant-atmosphere system and of plant production, as well as characteristics of agricultural products and materials, agrophysical measuring methods, soil degradation and remediation

Since Agrophysics became a widely practiced discipline of science there were already a number of agrophysical conferences organized. They gathered scientists which main research

interests focus on physics in agriculture. The conferences were organized as follows:

taken in Japan (R. Hatano) and China (T. Ren,).

8 Advances in Agrophysical Research

**4. Agrophysical conferences**

**•** Lublin, Poland 1976, B. Szot;

**•** Gödöllö, Hungary 1980, I. Husár;

**•** Bonn, Germany 1993, K.-H. Kromer;

**•** Lublin, Poland 1997, J. Gliński;

**•** Lublin, Poland 2005, R. Walczak; **•** Lublin, Poland 2011, J. Horabik;

**•** Prague, Czech Republic 1985, R. Řezniček; **•** Rostock, Germany 1989, H.-J. Hellebrand;

**•** Prague, Czech Republic 2001, J. Blahovec; **•** Louven, Belgium 2004, J. De Baerdemaeker;

problems.

Agrophysics was developed even in New Zealand by C.J. Studman.

proving that agrophysics is a world-wide recognized science discipline.

Institute of Agrophysic of the Polish Academy of Sciences is also the publisher of an outstand‐ ing scientific journal entitled "**International Agrophysics**". The editorial board states that: "the journal focuses on physical properties and processes affecting biomass production and processing. The main topics are: mass (water, air, plant nutrients) and energy (light, heat) transport in the soil-plant-atmosphere continuum, ways of their regulation in order to reach biomass of high quantity and quality. The description of new methods and devices for measurements of the physical properties of agro- and biomaterials are published. The journal is also open to wider aspects of environmental and agricultural physics". The present Editorin-Chief is prof. J. Gliński.

International Agrophysics is indexed by Journal Citation Reports with 1,574 impact factor.

A second journal published by the Institute of Agrophysics is "Acta Agrophysica". Acta Agrophysica has been published since 1993. At the beginning it contained mainly monogra‐ phies and dissertations which were published irregularly. From 2012 Acta Agrophysica is a quarterly. It publishes papers presenting the results of fundamental and applied studies from the field of application of physics for the solution of problems relating to the management and protection of the natural environment, sustainable agriculture, and food processing. Papers can be published both in Polish and English. The present Editor-in-Chief is prof. J. Horabik.

The third journal published by the Institute of Agrophysics is "Acta Agrophysica Monogra‐ phiae" which publishes reviewed papers based on original research results as well as mono‐ graphs pertaining to the field of agrophysics. The monographs are published in Polish or English. The present Editor-in-Chief is prof. J. Horabik.

The above mentioned journals are available in electronic versions on the internet.

## **6. Dictionaries and books, maps**

In order to facilitate international collaboration and allow unification of terminology, a number of bilingual and multilingual dictionary of agrophysical terms (nomenclature) was prepared under editorial supervision of prof. Ryszard Dębicki and prof. Jan Gliński. The following languages were taken into consideration: English, Russian, French, Spanish, German.

"Atlas of the Redox Properties of Arable Soils in Poland" prepared by Ostrowski, J.; Stęp‐ niewska, Z.; Stępniewski, W.; Gliński, J. was published 1996. It contains a wide range of data on soils in Poland presented in the form of cartographic maps. The Atlas gives a comprehensive information on soils in Poland and can be regarded as a research tool for studying spatial characteristics of agriculture. Practical application of the database lays in the power to generate, for the first time in the world, the thematic maps on spatial differentiation of the redox soil properties throughout the country. A set of these maps has been presented in the published atlas.

**•** to develop a scientific network with universities,

with a contribution to research projects,

obtain more funds for research.

**9. Polish Society of Agrophysics**

**Figure 3.** Location of PSA branches in Poland

European funds.

**•** to make the IA more attractive for students by combining post-graduate and doctoral studies

Introduction to Scientific Discipline Agrophysics — History and Research Objects

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11

**•** to establish a Foundation for Development of Agrophysical Research in order to be able to

The prolongation of the existence of the CoE and the consequence of this prolongation was a possibility for dynamic development of the structural base of the Institute. The full renovation of buildings as well as thorough exchange of research equipment was accomplished thanks to

Polish Society of Agrophysics (PSA) was founded in 1996 in Lublin. The initiator and the first president of PSA was prof. Bogusław Szot (1933 - 2012). He has been managing the Society until his death in October 2012. During his presidency ten branches in major scientific centers in Poland were established, where agrophysical investigations are performed (Fig. 3.). The Society is very active and every year it organizes meetings, seminars and symposia. Today PSA comprises over 360 members, among whom over 150 hold the title of full professor.

The main goal of the Society is to agglomerate researchers who conduct their research in the field of agrophysics. The Society has organized nine national and international conferences with over 1400 participants (115 of them from 29 countries outside Poland). Every conference has its own book of abstract, where the most recent results are presented. The most important papers are published in International Agrophysics and Acta Agrophysica – both journals

The last but most fundamental publication on Agrophysics is the "Encyclopedia of Agrophy‐ sics" edited by J. Gliński, J. Horabik and J. Lipiec by Springer in 2011. This book provides an up-to-date information on the physical properties and processes affecting the quality of the environment and plant production. Encyclopedia of Agrophysics is a publication comple‐ mentary to the Encyclopedia of Soil Science, (November 2007) which has been published in the field of Earth sciences series of Springer. The Encyclopedia presents a set of about 250 informative articles and ca 400 glossary terms covering all aspects of Agrophysics. It contains 450 illustrations on more than 1000 pages.

## **7. Data banks (soil probe bank)**

One of the comprehensive accomplishment of the Institute of Agrophysics PAS is the bank of soil samples collected all over Poland. The collection consists of over a thousand profiles (3 levels) and their full characteristics. This is a unique set of samples which can enable scientists to monitor changes of agriculture environment in Poland.

## **8. Agrophysics — European centre of excellence**

The Centre Of Excellence For Applied Physics In Sustainable Agriculture "AGROPHYSICS" was created on February 28-th. 2003, within the scheme of the 5-th. Framework Programme of the European Union. The project was realized for three years and ended on February 28th2006. The main goal of the project was to support the research potential of the region and strengthen its integration with the European Research Area.

The main points of the action plan of the CoE were:


**•** to develop a scientific network with universities,

information on soils in Poland and can be regarded as a research tool for studying spatial characteristics of agriculture. Practical application of the database lays in the power to generate, for the first time in the world, the thematic maps on spatial differentiation of the redox soil properties throughout the country. A set of these maps has been presented in the

The last but most fundamental publication on Agrophysics is the "Encyclopedia of Agrophy‐ sics" edited by J. Gliński, J. Horabik and J. Lipiec by Springer in 2011. This book provides an up-to-date information on the physical properties and processes affecting the quality of the environment and plant production. Encyclopedia of Agrophysics is a publication comple‐ mentary to the Encyclopedia of Soil Science, (November 2007) which has been published in the field of Earth sciences series of Springer. The Encyclopedia presents a set of about 250 informative articles and ca 400 glossary terms covering all aspects of Agrophysics. It contains

One of the comprehensive accomplishment of the Institute of Agrophysics PAS is the bank of soil samples collected all over Poland. The collection consists of over a thousand profiles (3 levels) and their full characteristics. This is a unique set of samples which can enable scientists

The Centre Of Excellence For Applied Physics In Sustainable Agriculture "AGROPHYSICS" was created on February 28-th. 2003, within the scheme of the 5-th. Framework Programme of the European Union. The project was realized for three years and ended on February 28th2006. The main goal of the project was to support the research potential of the region and strengthen

**•** to develop programmes aimed at significant technological applications, while preserving

**•** to intensify activities in attracting funds from the State Committee for Scientific Research (KBN; now – the Ministry of Science and Higher Education) under research grants,

**•** to concentrate on modern research fields with potential applications in industry,

**•** to expand the Institute's activities towards market-oriented research,

**•** to participate in European projects within European research programmes,

published atlas.

10 Advances in Agrophysical Research

450 illustrations on more than 1000 pages.

**7. Data banks (soil probe bank)**

to monitor changes of agriculture environment in Poland.

**8. Agrophysics — European centre of excellence**

its integration with the European Research Area.

high standard of fundamental research,

The main points of the action plan of the CoE were:

**•** to start co-operation with Polish industry and SMEs,


The prolongation of the existence of the CoE and the consequence of this prolongation was a possibility for dynamic development of the structural base of the Institute. The full renovation of buildings as well as thorough exchange of research equipment was accomplished thanks to European funds.

## **9. Polish Society of Agrophysics**

Polish Society of Agrophysics (PSA) was founded in 1996 in Lublin. The initiator and the first president of PSA was prof. Bogusław Szot (1933 - 2012). He has been managing the Society until his death in October 2012. During his presidency ten branches in major scientific centers in Poland were established, where agrophysical investigations are performed (Fig. 3.). The Society is very active and every year it organizes meetings, seminars and symposia. Today PSA comprises over 360 members, among whom over 150 hold the title of full professor.

**Figure 3.** Location of PSA branches in Poland

The main goal of the Society is to agglomerate researchers who conduct their research in the field of agrophysics. The Society has organized nine national and international conferences with over 1400 participants (115 of them from 29 countries outside Poland). Every conference has its own book of abstract, where the most recent results are presented. The most important papers are published in International Agrophysics and Acta Agrophysica – both journals edited at the Institute of Agrophysics PAS. Current information on the activities of PSA is distributed through its Information Bulletin.

achieved by publishing (Scientific Publishing House of FRNA) in the field of natural sciences and application of physics in agriculture. According to the up-to-date techniques, the Foun‐ dation proposed e-files i.e. electronic publications on CD and DVD instead traditionally printed books. The Foundation also sponsors various initiatives and initiates actions toward

Introduction to Scientific Discipline Agrophysics — History and Research Objects

http://dx.doi.org/10.5772/56982

13

For many years a workshop for prototype apparatus production was being organized at the Institute of Agophysics PAS in Lublin. A number of pioneer measuring techniques were elaborated and used in innovative apparatus. Both construction and production of this equipment was realized at the Institute. The founder and the first manager of the workshop

Under this activity a measuring systems for determination of moisture content and salinity of soil and other porous materials has been elaborated. The measuring techniques are based on the Time-Domain Reflectometry (TDR) which is worldwide patented. In the last years an innovative silo for drying and safe storage of rapeseed was constructed. The silo allows automated post-harvest drying, cooling, and storage of rapeseeds in neutral gas atmosphere to assure best quality of raw material for oil production. It prevents the development of heat processes as well as moulds and fungi growth in stored seeds. Also some prototype measuring apparatus were elaborated in order to evaluate quality parameters of fruit tissue especially

All the above mentioned activities, institutions and persons prove the necessity and usability of Agrophysics as a branch of applied science, which can help to solve current problems in

[1] Dobrzanski, B. (1986). Możliwości rozwoju agrofizyki. Wykład z okazji nadania tytu‐

łu Doktora Honoris Causa ART w Olsztynie, Kaseta video, ART, Olsztyn.

agriculture and which can benefit in progress of this part of economy.

Institute of Agrophysics Polish Academy of Sciences, Lublin, Poland

B. Dobrzański, S. Grundas and A. Stępniewski

popularization of agrophysics as science.

was M. Grochowicz, PhD.

apple tissue.

**Author details**

**References**

**12. Prototype apparatus and investigation methods**

## **10. Scientific Committee of Agrophysics of Polish Academy of Sciences**

The Committee of Agrophysics of Polish Academy of Sciences was established in 1981.

The Scientific Committees of the Polish Academy of Sciences are self-governing, nationwide representation of various disciplines or groups as well as interdisciplinary scientific problems integrating scholars throughout Poland. The scientific committee includes the Members of the Polish Academy of Sciences of the relevant specialty (outstanding scientists), eminent re‐ searchers representing universities, institutes of the Polish Academy of Sciences and the scientific institutes and research departments, as well as representatives of other institutions, including economic and social organizations. The scientific committees of the Polish Academy of Sciences are the most representative group of experts in the discipline.

The main task of the Scientific Committee of Agrophysics is to promote research of physical and physicochemical properties of the natural environment with particular emphasis on the system: soil-plant-atmosphere-machine-crops, agricultural-machine-food products. At present the chairman of the Committee is prof. Bohdan Dobrzański Jr.

Actually there are three sections operating within the structure of the Committee:


Since the beginning of its existence the Committee's special attention was directed to the integration of the scientific community and its involvement in the process of creatively solving important problems in agricultural research. The Committee in its activities focused also on identifying the main areas of research and science policy in the agrophysics. In previous years the Committee also financed research projects in the field of agrophysics. It has developed extensive cooperation with other committees working in the field of agricultural sciences. It also promoted international cooperation as a partner institution in organization of interna‐ tional conferences.

## **11. Foundation for Development of Agrophysical Sciences (FRNA)**

Foundation for Development of Agrophysical Sciences was established for the purpose of supporting and promoting the development of agrophysical research and activity of the Institute of Agrophysics PAS. The implementation of the main goals of the Foundation is achieved by publishing (Scientific Publishing House of FRNA) in the field of natural sciences and application of physics in agriculture. According to the up-to-date techniques, the Foun‐ dation proposed e-files i.e. electronic publications on CD and DVD instead traditionally printed books. The Foundation also sponsors various initiatives and initiates actions toward popularization of agrophysics as science.

## **12. Prototype apparatus and investigation methods**

For many years a workshop for prototype apparatus production was being organized at the Institute of Agophysics PAS in Lublin. A number of pioneer measuring techniques were elaborated and used in innovative apparatus. Both construction and production of this equipment was realized at the Institute. The founder and the first manager of the workshop was M. Grochowicz, PhD.

Under this activity a measuring systems for determination of moisture content and salinity of soil and other porous materials has been elaborated. The measuring techniques are based on the Time-Domain Reflectometry (TDR) which is worldwide patented. In the last years an innovative silo for drying and safe storage of rapeseed was constructed. The silo allows automated post-harvest drying, cooling, and storage of rapeseeds in neutral gas atmosphere to assure best quality of raw material for oil production. It prevents the development of heat processes as well as moulds and fungi growth in stored seeds. Also some prototype measuring apparatus were elaborated in order to evaluate quality parameters of fruit tissue especially apple tissue.

All the above mentioned activities, institutions and persons prove the necessity and usability of Agrophysics as a branch of applied science, which can help to solve current problems in agriculture and which can benefit in progress of this part of economy.

## **Author details**

edited at the Institute of Agrophysics PAS. Current information on the activities of PSA is

**10. Scientific Committee of Agrophysics of Polish Academy of Sciences**

The Scientific Committees of the Polish Academy of Sciences are self-governing, nationwide representation of various disciplines or groups as well as interdisciplinary scientific problems integrating scholars throughout Poland. The scientific committee includes the Members of the Polish Academy of Sciences of the relevant specialty (outstanding scientists), eminent re‐ searchers representing universities, institutes of the Polish Academy of Sciences and the scientific institutes and research departments, as well as representatives of other institutions, including economic and social organizations. The scientific committees of the Polish Academy

The main task of the Scientific Committee of Agrophysics is to promote research of physical and physicochemical properties of the natural environment with particular emphasis on the system: soil-plant-atmosphere-machine-crops, agricultural-machine-food products. At

**•** Section of Physics Application in Engineering of Agricultural Production and in Food

**•** Section for Physical Measurement Techniques for the Agricultural Environment Protection,

Since the beginning of its existence the Committee's special attention was directed to the integration of the scientific community and its involvement in the process of creatively solving important problems in agricultural research. The Committee in its activities focused also on identifying the main areas of research and science policy in the agrophysics. In previous years the Committee also financed research projects in the field of agrophysics. It has developed extensive cooperation with other committees working in the field of agricultural sciences. It also promoted international cooperation as a partner institution in organization of interna‐

**•** Section of Physical Methods of Evaluation of the Quality of Agricultural Products.

**11. Foundation for Development of Agrophysical Sciences (FRNA)**

Foundation for Development of Agrophysical Sciences was established for the purpose of supporting and promoting the development of agrophysical research and activity of the Institute of Agrophysics PAS. The implementation of the main goals of the Foundation is

The Committee of Agrophysics of Polish Academy of Sciences was established in 1981.

of Sciences are the most representative group of experts in the discipline.

present the chairman of the Committee is prof. Bohdan Dobrzański Jr.

Actually there are three sections operating within the structure of the Committee:

distributed through its Information Bulletin.

12 Advances in Agrophysical Research

Technology,

tional conferences.

B. Dobrzański, S. Grundas and A. Stępniewski

Institute of Agrophysics Polish Academy of Sciences, Lublin, Poland

## **References**

[1] Dobrzanski, B. (1986). Możliwości rozwoju agrofizyki. Wykład z okazji nadania tytu‐ łu Doktora Honoris Causa ART w Olsztynie, Kaseta video, ART, Olsztyn.

[2] Dobrzanski, B. (1981). Badania w zakresie fizyki i fizykochemii gleb. Kosmos, , 2, 135-139.

**Section 2**

**Physical Properties of Soil and Environment**


**Physical Properties of Soil and Environment**

[2] Dobrzanski, B. (1981). Badania w zakresie fizyki i fizykochemii gleb. Kosmos, , 2,

[3] Dobrzanski, B, Dechnik, I, & Glinski, J. (1979). Rozwój badań agrofizycznych w

[4] Dobrzanski, B, Glinski, J, & Szot, B. (1988). Agrophysical investigations in Poland at present and in future. Physical properties of agricultural materials and products.

[6] Haman, J, Horabik, J, & Pukos, A. (1985). Mechanical investigations of agricultural materials in the Institute of Agrophysics. Zesz. Probl. Post. Nauk Roln., z. , 304, 9-16.

[7] Szot, B. Dobrzański jr B., (1995). Agrofizyka dla techniki rolniczej. Zesz. Probl. Post.

[8] Tanner, C. B, & Simonson, R. W. (1993). Franklin Hiram King- Pioneer Scientist. Soil

[5] Glinski, J, Horabik, J, & Lipiec, J. (2011). Encyclopedia of Agrophysics. Springer.

135-139.

14 Advances in Agrophysical Research

Polsce. Post. Nauk Roln., 5.

Nauk Roln., z. , 424, 79-86.

[9] http://www.agrophys.ru/

[10] http://www.ipan.lublin.pl/

Hemisphere Publ. Corp., New York, , 873-976.

Science Society of America Journal , 57(1)

[11] http://www.international-agrophysics.org/

[13] http://www.acta-agrophysica-monographiae.org/

[12] http://www.acta-agrophysica.org/

[14] http://www.komagrof.pan.pl/

**Chapter 2**

**Aquametry in Agrophysics**

Andrzej Wilczek

**1. Introduction**

http://dx.doi.org/10.5772/52505

Wojciech Skierucha, Agnieszka Szypłowska and

Aquametry is a part of metrology that uses the available measurement techniques in the measurement of water content in solid, liquid and heterogeneous materials. A similar branch of metrology, called hygrometry, deals with determination of the water vapour con‐ tent in air and other gases (Kraszewski, 2001). The aim of agrophysics is to apply physical methods and techniques for studies of materials and processes which take place in agricul‐ ture. Possible test objects may therefore include soil, fruit, vegetables, intermediate and final

Historically, the primary application of aquametry in agrophysics is the measurement of soil water content. The available soil water content measurement techniques are evolving to fol‐ low the technological development in metrology. Soil is an inhomogeneous and complex medium in physical, chemical and biological aspects, which makes determination of soil wa‐ ter content a difficult technical and methodological problem. New moisture measurement methodologies and techniques, developed for the purpose of soil testing, in many cases have been later adapted to other agrophysical fields of interest, including storage of grain, conservation and quality testing of food products, transportation, climate change research

Water is the basic biological solvent and an absolutely necessary component of every life form on Earth. The shortage of water is the main growth limiting factor for plants and other organisms in arid regions. Sufficient continuous supply of fresh water is obviously a funda‐ mental necessity for human and animal life. Because water is a deficit resource in many parts of the world, the sustainable and harmonious development of societies needs reasona‐ ble and responsible water management policy. Continuous long-term monitoring of soil moisture on local and global scales, extremely significant for agriculture (including irriga‐

> © 2013 Skierucha et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2013 Skierucha et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

products of the food industry, grain, oils, etc.

and safety measures against floods and landslides.

## **Chapter 2**

## **Aquametry in Agrophysics**

Wojciech Skierucha, Agnieszka Szypłowska and Andrzej Wilczek

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/52505

## **1. Introduction**

Aquametry is a part of metrology that uses the available measurement techniques in the measurement of water content in solid, liquid and heterogeneous materials. A similar branch of metrology, called hygrometry, deals with determination of the water vapour con‐ tent in air and other gases (Kraszewski, 2001). The aim of agrophysics is to apply physical methods and techniques for studies of materials and processes which take place in agricul‐ ture. Possible test objects may therefore include soil, fruit, vegetables, intermediate and final products of the food industry, grain, oils, etc.

Historically, the primary application of aquametry in agrophysics is the measurement of soil water content. The available soil water content measurement techniques are evolving to fol‐ low the technological development in metrology. Soil is an inhomogeneous and complex medium in physical, chemical and biological aspects, which makes determination of soil wa‐ ter content a difficult technical and methodological problem. New moisture measurement methodologies and techniques, developed for the purpose of soil testing, in many cases have been later adapted to other agrophysical fields of interest, including storage of grain, conservation and quality testing of food products, transportation, climate change research and safety measures against floods and landslides.

Water is the basic biological solvent and an absolutely necessary component of every life form on Earth. The shortage of water is the main growth limiting factor for plants and other organisms in arid regions. Sufficient continuous supply of fresh water is obviously a funda‐ mental necessity for human and animal life. Because water is a deficit resource in many parts of the world, the sustainable and harmonious development of societies needs reasona‐ ble and responsible water management policy. Continuous long-term monitoring of soil moisture on local and global scales, extremely significant for agriculture (including irriga‐

© 2013 Skierucha et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Skierucha et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

tion), environmental protection, meteorology, climatology, scientific research and water management, requires reliable measurement techniques. The development of remote and proximal soil moisture determination methods is therefore one of the most important aims of aquametry.

Another useful quantity is the volumetric water content given by the relation

lated on a wet basis as follows

*<sup>θ</sup><sup>v</sup>* <sup>=</sup> *<sup>V</sup> <sup>w</sup> Vb*

*<sup>θ</sup><sup>v</sup>* <sup>=</sup>*<sup>ξ</sup> <sup>ρ</sup><sup>b</sup> ρw*

each other and another compatible polar chemical groups.

other chemical constituents of a given material.

where *Vw* is the volume of water contained in a given body and *Vb* is the bulk volume of this body. Knowing the bulk density of the tested material, *ρ<sup>b</sup>* =*mb* / *Vb* , and the density of water, *ρw*, the volumetric water content may be expressed by the mass water content calcu‐

The total amount of water contained in a given body does not fully determine all of its mois‐ ture related properties. The structure and chemical composition of a given body can greatly influence the properties of contained water. The molecule of water, consisting of two hydro‐ gen atoms bound to an atom of oxygen, exhibits polar structure. It may be described as a regular tetrahedron, with the oxygen atom in the centre and the hydrogen atoms with parti‐ al positive charges in two corners. Free corners of the tetrahedron are occupied by two elec‐ tron orbitals. Effectively, though a water molecule is not electrically charged, it possesses an electrical dipole moment. Water molecules are thus enabled to form hydrogen bonds with

Because of the unique properties of water molecules, generally it is possible to distinguish three states of water in a moist material (Hillel, 2004; Lewicki, 2004; Chen and Or, 2006):

**1.** Bound water – consisting of water molecules bound by hydrogen bonds to a macromo‐ lecule (so called structure water – its molecules are immobilised and become structural parts of a macromolecule) and of oriented water molecules forming hydration shells around ions, polar chemical groups and whole macromolecules (so called hydration water). Number of water molecules in a hydration shell, as well as their orientation, dis‐ tortion and number of layers depend on the surface charge density of an ion or on a structure of a macromolecule in question. Furthermore, even non-polar compounds in‐ teract with water, affecting the distribution and orientation of surrounding water mole‐

**2.** Capillary water – because water exhibits surface tension, in non-hydrophobic porous materials water can be held in the pores through a capillary pressure, defined as a dif‐ ference of pressures above and below the surface of the water meniscus. It causes the effect of a capillary rise above the free water surface to the height defined by the surface tension, contact angle, capillary radius and the difference between the water and gas (air) densities. Water is more easily held in smaller pores than in large ones. Capillary

water is at equilibrium with the films of bound water adsorbed on the surfaces.

**3.** Free water – movement of its molecules is not constrained by any kinds of bonds with

cules – the effect is called hydrophobic hydration (Lewicki, 2004).

(3)

19

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505

(4)

The practical agricultural applications of water content determination are not restricted to soil measurements. The storage of grain, seeds and other crops, as well as their processing and resultant food products, usually require control of moisture level to prevent spoilage and proliferation of pests, to preserve their quality and extend their shelf life, and to ensure appropriate technological processing conditions. Another fundamental application of aqua‐ metry is therefore the evaluation of the state and content of water in various materials of ag‐ ricultural origin, including food products. Because of high variability of such materials, which may be liquids, solids, porous materials or heterogeneous mixtures of complicated structure and chemical composition, the development of appropriate aquametry techniques may become a challenging endeavour.

Due to the recent technological development in the fields of electronics, informatics, micro‐ wave techniques and mobile communication, there is a significant progress in indirect die‐ lectric measurement methods, especially the broadband spectroscopic techniques. These methods enable fast, selective and non-destructive measurements using portable meters and sensors that can be applied in real time testing during production processes and monitoring of storage of various agricultural materials and food products. On the other hand, there are several significant obstacles hampering the development of effective dielectric techniques for determination of moisture content and related material properties. The main difficulties lie in the necessity of performing basic research to understand water-involving physical and chemical processes at micro- and macroscopic scales, mechanisms of polarization and influ‐ ence of electromagnetic waves on studied materials, development of selective sensor techni‐ ques and achieving the required accuracy.

#### **1.1. Physical fundamentals and definitions**

The amount of water in a given body may be described by the mass or volume of water rela‐ tive to the mass or volume of the whole moist object or just the appropriate dry mass (Kras‐ zewski, 2001; Hillel, 2004). On a wet basis, the mass water content of a body is equal to the mass of the water, *mw*, divided by the bulk mass of the moist body, *mb*, which is the sum of the mass of the water and the mass of the dry material, *md*

$$\xi = \frac{m\_v}{m\_b} \; \; \; m\_b = m\_w + m\_d \tag{1}$$

The mass water content on a dry basis is defined as the ratio of the mass of water to the mass of the dry material

$$
\eta = \frac{m\_w}{m\_d} \tag{2}
$$

Another useful quantity is the volumetric water content given by the relation

tion), environmental protection, meteorology, climatology, scientific research and water management, requires reliable measurement techniques. The development of remote and proximal soil moisture determination methods is therefore one of the most important aims

The practical agricultural applications of water content determination are not restricted to soil measurements. The storage of grain, seeds and other crops, as well as their processing and resultant food products, usually require control of moisture level to prevent spoilage and proliferation of pests, to preserve their quality and extend their shelf life, and to ensure appropriate technological processing conditions. Another fundamental application of aqua‐ metry is therefore the evaluation of the state and content of water in various materials of ag‐ ricultural origin, including food products. Because of high variability of such materials, which may be liquids, solids, porous materials or heterogeneous mixtures of complicated structure and chemical composition, the development of appropriate aquametry techniques

Due to the recent technological development in the fields of electronics, informatics, micro‐ wave techniques and mobile communication, there is a significant progress in indirect die‐ lectric measurement methods, especially the broadband spectroscopic techniques. These methods enable fast, selective and non-destructive measurements using portable meters and sensors that can be applied in real time testing during production processes and monitoring of storage of various agricultural materials and food products. On the other hand, there are several significant obstacles hampering the development of effective dielectric techniques for determination of moisture content and related material properties. The main difficulties lie in the necessity of performing basic research to understand water-involving physical and chemical processes at micro- and macroscopic scales, mechanisms of polarization and influ‐ ence of electromagnetic waves on studied materials, development of selective sensor techni‐

The amount of water in a given body may be described by the mass or volume of water rela‐ tive to the mass or volume of the whole moist object or just the appropriate dry mass (Kras‐ zewski, 2001; Hillel, 2004). On a wet basis, the mass water content of a body is equal to the mass of the water, *mw*, divided by the bulk mass of the moist body, *mb*, which is the sum of

The mass water content on a dry basis is defined as the ratio of the mass of water to the

*<sup>η</sup>* <sup>=</sup> *mw md*

*mb* , *mb* <sup>=</sup>*mw* <sup>+</sup> *md* (1)

(2)

of aquametry.

18 Advances in Agrophysical Research

may become a challenging endeavour.

ques and achieving the required accuracy.

**1.1. Physical fundamentals and definitions**

mass of the dry material

the mass of the water and the mass of the dry material, *md*

*<sup>ξ</sup>* <sup>=</sup> *mw*

$$
\Theta\_v = \frac{V\_w}{V\_b} \tag{3}
$$

where *Vw* is the volume of water contained in a given body and *Vb* is the bulk volume of this body. Knowing the bulk density of the tested material, *ρ<sup>b</sup>* =*mb* / *Vb* , and the density of water, *ρw*, the volumetric water content may be expressed by the mass water content calcu‐ lated on a wet basis as follows

$$
\Theta\_v = \xi \frac{\rho\_b}{\rho\_w} \tag{4}
$$

The total amount of water contained in a given body does not fully determine all of its mois‐ ture related properties. The structure and chemical composition of a given body can greatly influence the properties of contained water. The molecule of water, consisting of two hydro‐ gen atoms bound to an atom of oxygen, exhibits polar structure. It may be described as a regular tetrahedron, with the oxygen atom in the centre and the hydrogen atoms with parti‐ al positive charges in two corners. Free corners of the tetrahedron are occupied by two elec‐ tron orbitals. Effectively, though a water molecule is not electrically charged, it possesses an electrical dipole moment. Water molecules are thus enabled to form hydrogen bonds with each other and another compatible polar chemical groups.

Because of the unique properties of water molecules, generally it is possible to distinguish three states of water in a moist material (Hillel, 2004; Lewicki, 2004; Chen and Or, 2006):


A physical thermodynamic quantity describing the state of water in a given body (liquid or solid) is called the water activity coefficient, *aw* (Lewicki, 2004). It is defined as the ratio of the water vapour pressure in a given material, *p*, to the vapour pressure of pure free water, *p*0, at the same temperature and total pressure

$$a\_w = \frac{p}{p\_0} \tag{5}$$

**2. Measurement methods and equipment**

examinations.

*2.1.1. Selectivity*

To properly and comprehensively characterise the influence of water contained in a given object on the properties of the said object, several parameters must be determined. In case of agricultural materials and food products, the most important of those parameters are: water content (by mass or by volume), water activity/potential and in case of soils also sal‐ inity, oxygenation and temperature (Malicki, 1999).Soil, being a porous three-phase body comprising of various mineral particles of different size and composition (clay, silt and sand particles) with soil water and air filling the pores, containing a countless number of various chemical compounds and organic matter, like microorganisms, flora and fauna spe‐ cies, is surely one of the most complex and variable medium in Nature. The accurate meas‐ urement of physical properties of such materials is thus a difficult challenge. Many of the modern aquametry techniques, appropriate for the soil, are also suitable for other materi‐ als like grain and food products, which are not as complex as soil. Therefore, the measure‐ ment methods and equipment described in this section will pertain mostly to soil water

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 21

From the agrophysical point of view, determining the status of water in soil and other po‐ rous materials is extremely important because each phenomenon and process taking place in such medium depends on its water-related properties (Blahovec, 2011). To achieve this goal, various methods and techniques have been developed, including sampling, non-de‐

The measurement of physical quantities is rarely direct, that is the value of a quantity in question is usually inferred from another quantity or quantities determined during the measurement process. For example, soil water content may be determined from measure‐ ments of mass of the moist and dry sample, electrical resistance or capacity, neutron scatter‐ ing, gamma-ray absorption or dielectric permittivity of the soil, depending on the applied measurement technique. The conversion function between the intermediary and the target quantities is called the calibration function. The critical issue in the selection of the measure‐ ment method is its selectivity, that is the lack of influence on the final result from factors other than the desired quantity. Good selectivity enables the usage of general calibrations,

The physical quantity enabling selective determination of soil water content in several mod‐ ern measurement techniques is dielectric permittivity. The relative dielectric permittivity of water for frequencies of the electric field below the relaxation frequency of 18 GHz is equal to about 80, while for the soil solid phase its value is of about 4 – 6. Therefore, the dielectric permittivity of soil is strongly dependent on the water content. The influence of the temper‐

structive proximal and remote sensing, automatic monitoring systems, etc.

**2.1. Common issues of water content measurement techniques**

valid for many types of soil and independent of local conditions.

Water activity is especially useful in food industries, in processing technology and to assess food safety. The water activity is greatly affected by the amount of solute molecules and their interaction with water. For example, the more of the water molecules are bounded by the solute molecules, the lower the *aw* is. The proliferation of microorganisms, causing spoil‐ age of food, depends on the value of the water activity. For given microbial species, there is an inhibiting value of *aw*, below which the proliferation is ceased. This is realised in many food preservation methods, such as freezing, salting and drying (Tapia et al., 2007).

To characterise the state of water in porous bodies such as soil, a quantity related to water activity, called water potential, *ϕ* , is defined as (Or and Wraith, 2002):

$$
\phi = \phi\_m + \phi\_o + \phi\_g + \phi\_p = RT \ln \frac{p}{p\_0} \tag{6}
$$

Here R = 8.31 JK-1mol-1 is the gas constant and *T* is the thermodynamic temperature. The definition above pertains to the total water potential, which is the sum of several terms:


To express water potential in terms of pressure, one needs to multiply it by water density. Because pressure of soil water may be lower than the atmospheric, matric potential may possess negative values. Disregarding the negative sign, water potential is called tension or suction. Water potential governs the direction of the water flow, that is water tends to flow from areas with high water potential (or low suction) towards areas, in which the potential is lower (or the suction higher). For example, when considering the soil-plant-atmosphere continuum, the differences in water potential between soil and roots determines the absorp‐ tion of water by plants.

## **2. Measurement methods and equipment**

To properly and comprehensively characterise the influence of water contained in a given object on the properties of the said object, several parameters must be determined. In case of agricultural materials and food products, the most important of those parameters are: water content (by mass or by volume), water activity/potential and in case of soils also sal‐ inity, oxygenation and temperature (Malicki, 1999).Soil, being a porous three-phase body comprising of various mineral particles of different size and composition (clay, silt and sand particles) with soil water and air filling the pores, containing a countless number of various chemical compounds and organic matter, like microorganisms, flora and fauna spe‐ cies, is surely one of the most complex and variable medium in Nature. The accurate meas‐ urement of physical properties of such materials is thus a difficult challenge. Many of the modern aquametry techniques, appropriate for the soil, are also suitable for other materi‐ als like grain and food products, which are not as complex as soil. Therefore, the measure‐ ment methods and equipment described in this section will pertain mostly to soil water examinations.

From the agrophysical point of view, determining the status of water in soil and other po‐ rous materials is extremely important because each phenomenon and process taking place in such medium depends on its water-related properties (Blahovec, 2011). To achieve this goal, various methods and techniques have been developed, including sampling, non-de‐ structive proximal and remote sensing, automatic monitoring systems, etc.

#### **2.1. Common issues of water content measurement techniques**

## *2.1.1. Selectivity*

A physical thermodynamic quantity describing the state of water in a given body (liquid or solid) is called the water activity coefficient, *aw* (Lewicki, 2004). It is defined as the ratio of the water vapour pressure in a given material, *p*, to the vapour pressure of pure free water,

Water activity is especially useful in food industries, in processing technology and to assess food safety. The water activity is greatly affected by the amount of solute molecules and their interaction with water. For example, the more of the water molecules are bounded by the solute molecules, the lower the *aw* is. The proliferation of microorganisms, causing spoil‐ age of food, depends on the value of the water activity. For given microbial species, there is an inhibiting value of *aw*, below which the proliferation is ceased. This is realised in many

To characterise the state of water in porous bodies such as soil, a quantity related to water

Here R = 8.31 JK-1mol-1 is the gas constant and *T* is the thermodynamic temperature. The definition above pertains to the total water potential, which is the sum of several terms:

**•** matric potential, denoted *ϕm*, which depends on the capillary pressure and the adsorption

**•** osmotic pressure potential, *ϕo*, describing the influence of solutes on the state of water;

**•** gravitational potential, *ϕg*, arising from the gravitational force being exerted on the water

**•** pressure potential, *ϕp*, defined as the hydrostatic pressure exerted by unsupported water

To express water potential in terms of pressure, one needs to multiply it by water density. Because pressure of soil water may be lower than the atmospheric, matric potential may possess negative values. Disregarding the negative sign, water potential is called tension or suction. Water potential governs the direction of the water flow, that is water tends to flow from areas with high water potential (or low suction) towards areas, in which the potential is lower (or the suction higher). For example, when considering the soil-plant-atmosphere continuum, the differences in water potential between soil and roots determines the absorp‐

this term is often neglected for porous bodies with no diffusion barriers,

<sup>+</sup> *<sup>ϕ</sup><sup>p</sup>* <sup>=</sup>*RT* ln *<sup>p</sup>*

*p*0

(5)

(6)

*aw* <sup>=</sup> *<sup>p</sup> p*0

food preservation methods, such as freezing, salting and drying (Tapia et al., 2007).

activity, called water potential, *ϕ* , is defined as (Or and Wraith, 2002):

*ϕ* =*ϕ<sup>m</sup>* + *ϕ<sup>o</sup>* + *ϕ<sup>g</sup>*

*p*0, at the same temperature and total pressure

20 Advances in Agrophysical Research

of water on the surfaces of solid particles,

(i.e., saturating the soil) overlying a point of interest.

confined in a given porous body,

tion of water by plants.

The measurement of physical quantities is rarely direct, that is the value of a quantity in question is usually inferred from another quantity or quantities determined during the measurement process. For example, soil water content may be determined from measure‐ ments of mass of the moist and dry sample, electrical resistance or capacity, neutron scatter‐ ing, gamma-ray absorption or dielectric permittivity of the soil, depending on the applied measurement technique. The conversion function between the intermediary and the target quantities is called the calibration function. The critical issue in the selection of the measure‐ ment method is its selectivity, that is the lack of influence on the final result from factors other than the desired quantity. Good selectivity enables the usage of general calibrations, valid for many types of soil and independent of local conditions.

The physical quantity enabling selective determination of soil water content in several mod‐ ern measurement techniques is dielectric permittivity. The relative dielectric permittivity of water for frequencies of the electric field below the relaxation frequency of 18 GHz is equal to about 80, while for the soil solid phase its value is of about 4 – 6. Therefore, the dielectric permittivity of soil is strongly dependent on the water content. The influence of the temper‐ ature in many cases may be neglected (Skierucha, 2009). The salinity of the soil may also in‐ terfere with the water content measurement, however its influence is negligible for the electric field frequencies of the order of 400 MHz and higher (Skierucha and Wilczek, 2010). The dielectric measurement methods, described in detail in section 2.3.2, are therefore high‐ ly selective and give reliable results for various field conditions.

**Name of the measurement method**

> TDR (time domain reflectometry)

FDR (frequency domain reflectometry)

Neutron scattering

Electrical resistance blocks

2011)

**Directly measured quantity, physical principle, soil**

Velocity of propagation of the electromagnetic wave (step or needle pulse) along the metallic parallel or coaxial waveguide (TDR probe) fully inserted into the soil. It is very well correlated with the real part of the soil complex dielectric permittivity as well as the amount of water in soil (Topp et al., 1980; Noborio et al., 1999).

Attenuation of the electromagnetic wave during its travel in the TDR probe, which results mainly from the soil electrical conductivity dependent ion conduction. Signal attenuation is correlated with the soil bulk electrical conductivity and soil salinity (electrical conductivity of soil extract) (Malicki and Walczak, 1999;

Phase shift (dependent on soil bulk dielectric

permittivity) and amplitude attenuation (dependent on soil salinity) of an electrical signal a probe inserted into the soil treated as a lossy capacitor. Measurement is done in a single frequency generated by the internal probe oscillator (50-150 MHz) (Veldkamp and O'Brien,

Number slow neutrons that are produced from the collision of fast neutrons with hydrogen molecules in soil, which is linearly related to the soil volumetric water content. Fast neutron generator and the counter are

transducer in a water filled tube connected with soil matrix by a porous cap. The measured physical quantity is a matrix potential of soil water, which is an basic element of the total potential of water in the soil

Electrical resistance, measured with an alternating current bridge (usually ≈ 1000 Hz) of electrodes encased in some type of porous material (gypsum, nylon fabric, fiberglass) that within about two days will reach a quasi-equilibrium state with the soil. This method determines soil water content and water potential as a function of electrical resistance (Spaans and Baker,

**Table 1.** Selection of the most popular non-destructive soil water status measurement methods, from (Skierucha,

installed in the vertical access tube for the measurements in different layers of soil (Evett and **Remarks**

geometry.

Commonly recognized alternative for the thermogravimetric method, instruments are still very expensive, usually no site calibration required.

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 23

Not applicable for very saline soils and long probe rods, limited accuracy caused by the possible change of the TDR probe

Requires soil site calibration, probes and meters are commercially available and cheaper than TDR

instrumentation, low power consumption as compared to

Limited range of work (down to

requires frequent servicing (air bubbles),in drought conditions water moves from the tensiometer to the soil.

Sensitive to soil salinity and temperature, requires soil specific calibration, very economic and field installations can work for several years, supplementary to tensiometers in the range up to

TDR technique.

Requires soil site calibration ,precise but expensive, additional cost with special licensing, operator training, handling, radiation materials waste disposal, health

hazard.

about -85 kPa),


**property measured and references**

Robinson et al., 2003).

2000).

Steiner, 1995).

Tensiometry Suction force or pressure exerted on a pressure

1992; Hillel, 2004).

(Mullins, 2001; Sisson et al., 2002).

Salinity of the soil may also be determined by electrical measurements. Salts dissolved in the soil water are the sources of ions, which enable the electric current conduction. Therefore, the soil electrical conductivity may be used as a salinity measure. Electrical conductivity is highly dependent not only on the concentration of ions, but also on temperature and water content. However, there are integrated dielectric sensors that enable simultaneous measure‐ ments of soil moisture, temperature and electrical conductivity.

#### *2.1.2. Resolution and sampling*

In case of inhomogeneous medium, the volume of the sample, on which the measurement is performed, may influence the final result. Because of the spatial and temporal variability of the soil, the measured values may differ even for points in proximity to each other.

Soil water content may be examined at a point, field, catchment, country or global scale. The spatial and temporal resolution and coverage of the measurements depend on the measure‐ ment and monitoring technique, selection of which is dependent on the purpose of the measurements. For example, satellite sensing provides global coverage with spatial resolu‐ tion of many kilometres, while proximal techniques give soil moisture values close to a point scale, with the spatial and temporal coverage limited by the number of monitoring sta‐ tions and the chosen time schedule for the measurements (Vereecken et al., 2008; Skierucha and Wilczek, 2010).

Several soil water content measurement techniques, like the thermogravimetric method de‐ scribed in section 2.2, require acquisition of traditional samples. The process is usually dis‐ ruptive to the surroundings and may disturb the sample itself. The extraction, transport and processing of the sample may introduce errors, which may be reduced by increasing the number and volume of taken samples. Such measurement methods are usually laborious and time-consuming, which makes them unsuitable for monitoring applications.

#### *2.1.3. Non-destructive measurements*

There is a number of measurement techniques which do not require extraction of samples and provide means for non-destructive or even non-invasive testing.

Non-destructive measurement methods do not disturb the sample, enabling repetitive ex‐ aminations of the same object. However, installation of probes and measurement stations in the soil may still be required. The advantage is that after the initial disturbance during the installation, the act of measurement do not affect the tested sample nor its surroundings. Such techniques are therefore suitable even for long-term monitoring purposes.


ature in many cases may be neglected (Skierucha, 2009). The salinity of the soil may also in‐ terfere with the water content measurement, however its influence is negligible for the electric field frequencies of the order of 400 MHz and higher (Skierucha and Wilczek, 2010). The dielectric measurement methods, described in detail in section 2.3.2, are therefore high‐

Salinity of the soil may also be determined by electrical measurements. Salts dissolved in the soil water are the sources of ions, which enable the electric current conduction. Therefore, the soil electrical conductivity may be used as a salinity measure. Electrical conductivity is highly dependent not only on the concentration of ions, but also on temperature and water content. However, there are integrated dielectric sensors that enable simultaneous measure‐

In case of inhomogeneous medium, the volume of the sample, on which the measurement is performed, may influence the final result. Because of the spatial and temporal variability of

Soil water content may be examined at a point, field, catchment, country or global scale. The spatial and temporal resolution and coverage of the measurements depend on the measure‐ ment and monitoring technique, selection of which is dependent on the purpose of the measurements. For example, satellite sensing provides global coverage with spatial resolu‐ tion of many kilometres, while proximal techniques give soil moisture values close to a point scale, with the spatial and temporal coverage limited by the number of monitoring sta‐ tions and the chosen time schedule for the measurements (Vereecken et al., 2008; Skierucha

Several soil water content measurement techniques, like the thermogravimetric method de‐ scribed in section 2.2, require acquisition of traditional samples. The process is usually dis‐ ruptive to the surroundings and may disturb the sample itself. The extraction, transport and processing of the sample may introduce errors, which may be reduced by increasing the number and volume of taken samples. Such measurement methods are usually laborious

There is a number of measurement techniques which do not require extraction of samples

Non-destructive measurement methods do not disturb the sample, enabling repetitive ex‐ aminations of the same object. However, installation of probes and measurement stations in the soil may still be required. The advantage is that after the initial disturbance during the installation, the act of measurement do not affect the tested sample nor its surroundings.

and time-consuming, which makes them unsuitable for monitoring applications.

Such techniques are therefore suitable even for long-term monitoring purposes.

and provide means for non-destructive or even non-invasive testing.

the soil, the measured values may differ even for points in proximity to each other.

ly selective and give reliable results for various field conditions.

ments of soil moisture, temperature and electrical conductivity.

*2.1.2. Resolution and sampling*

22 Advances in Agrophysical Research

and Wilczek, 2010).

*2.1.3. Non-destructive measurements*

**Table 1.** Selection of the most popular non-destructive soil water status measurement methods, from (Skierucha, 2011)

On the other hand, non-invasive techniques do not introduce any disturbance of the tested material. Particularly, they do not use any probes which must be installed in the measure‐ ment site. Non-invasive methods include techniques such as airborne and satellite remote sensing (Jackson et al., 1996) or near infra-red reflectance spectroscopy (NIRS) (Cécillon et al., 2009). Remote techniques usually examine only the topsoil and require ground measure‐ ments for the proper calibration. However, they are irreplaceable for the monitoring of the soil properties on a global scale.

by placing in an oven at temperature of 105°C for 24 hours (Hillel, 2004). However, this is still an arbitrary standard. It is difficult to completely dry a material containing microscopic pores and solid particles which easily adsorb water. Some soils, especially those containing much clay, may still hold some water even after the standard drying. On the other hand, some soils may contain many compounds which tend to decompose and evaporate along with water, while the sample is in the oven. The evaporation of other compounds beside

Another source of error in the moisture content measurement by the thermogravimetric method is the extraction of a sample and its transport to the laboratory, where usually the oven is located. Each disturbance of the sample during this process may cause errors. Fur‐ thermore, in this method the sample is irreversibly destroyed during the drying process, al‐

There exist a method of drying alternative to the oven, in which the sample is placed in a container and impregnated with alcohol (Hillel, 2004). The alcohol is then burned off, what

The thermogravimetric method, despite being destructive, laborious, time-consuming, prone to errors and completely impractical for monitoring purposes, is commonly regarded as a reference method. Most importantly, it is used as a calibration standard for other mois‐

One of the most important chemical method of water content measurement is the Karl Fischer titration(Isengard, 2001). It is regarded as a reference method for determining the

In the volumetric variation of this technique, a sample of tested material, i.e. the analyte, is placed in a titration cell along with the working medium and the titrant solution. The chemi‐ cal components added to the analyte are: alcohol (ROH, usually methanol), sulphur dioxide (SO2), a base (B, usually imidazole) and iodine (I2). The overall reaction that occurs in the

In the net reaction, one mole of iodine is consumed per one mole of water from the analyte. The amount of water is therefore measured by the consumption of iodine. In the coulometric variation of this method, iodine is not added in the solution, but it is produced in the cell

The end-point of the reaction is detected through electrochemical means. There are two plat‐ inum electrodes placed in the titration cell. In the so called bipotentiometric technique, a constant current is maintained on the electrodes and the voltage is monitored. In the biam‐ perometric variation, the voltage is kept constant and the current is measured. When all the



Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 25

3B <sup>+</sup> ROH <sup>+</sup> SO2 <sup>+</sup> I2 <sup>+</sup> H2O→3BH<sup>+</sup> <sup>+</sup> ROSO3

water causes overestimation of the initial water content of the sample.

causes the evaporation of water. This method may be used in the field.

lowing only one measurement of a given sample.

ture measurement techniques.

moisture content of food products.

*2.2.2. Karl Fischer titration*

titration cell is as follows:

from iodide by anodic oxidation.

Non-destructive measurement methods have been adapted by agrophysics from various branches of science and industry. Therefore, the physical principles of those techniques vary greatly, from optical to electrical and nuclear methods. Despite the underlying measurement principle, the sensor device suitable for non-destructive and repetitive testing should pos‐ sess several universal features, such as a data-logging option, a power supply enabling longterm operation without recharging and the communication capability for the remote configuration and transferring of the measurement results to the user. An overview of vari‐ ous non-destructive soil water measurement methods is presented in Table 1. The measur‐ ing principle of each technique is briefly described, along with the most important advantages and limitations.

Because the determination of soil water status requires measurement of several parameters, the construction of integrated sensors, which measure several soil properties at the same time and on the same sample volume, becomes increasingly popular. For example, TDR and FDR methods enable the development of the soil water content and soil salinity measure‐ ment device, with the possibility of an addition of a temperature sensor (Skierucha et al., 2006).

#### **2.2. Direct methods of water content measurement**

#### *2.2.1. Thermogravimetric method*

The traditional and standard water content measurement technique, called the thermogra‐ vimetric method, is based on a very simple concept of weighting a sample of a moist mate‐ rial, drying it and then weighting again. The difference between the mass of the moist and the dry material, equal to the mass of water evaporated from the original sample, divided by the mass of the dry material (assuming all of the water evaporated during the drying process), is an exact definition of mass water content on a dry basis (Equation 2). This quantity is also called gravimetric water content. Volumetric water content, when re‐ quired, may be then easily calculated from the mass water content, according to relations presented in section 1.1.

However, the practical application of the thermogravimetric method is not so simple. First, a sample of a material under test needs to be collected. In case of soil testing, this process is invasive and disruptive to the soil profile and its surroundings. To achieve comparative re‐ sults, the process of drying needs to be standardised. The temperature and time length of the drying should be adjusted to the specifics of a given material. For soils, a sample is dried by placing in an oven at temperature of 105°C for 24 hours (Hillel, 2004). However, this is still an arbitrary standard. It is difficult to completely dry a material containing microscopic pores and solid particles which easily adsorb water. Some soils, especially those containing much clay, may still hold some water even after the standard drying. On the other hand, some soils may contain many compounds which tend to decompose and evaporate along with water, while the sample is in the oven. The evaporation of other compounds beside water causes overestimation of the initial water content of the sample.

Another source of error in the moisture content measurement by the thermogravimetric method is the extraction of a sample and its transport to the laboratory, where usually the oven is located. Each disturbance of the sample during this process may cause errors. Fur‐ thermore, in this method the sample is irreversibly destroyed during the drying process, al‐ lowing only one measurement of a given sample.

There exist a method of drying alternative to the oven, in which the sample is placed in a container and impregnated with alcohol (Hillel, 2004). The alcohol is then burned off, what causes the evaporation of water. This method may be used in the field.

The thermogravimetric method, despite being destructive, laborious, time-consuming, prone to errors and completely impractical for monitoring purposes, is commonly regarded as a reference method. Most importantly, it is used as a calibration standard for other mois‐ ture measurement techniques.

#### *2.2.2. Karl Fischer titration*

On the other hand, non-invasive techniques do not introduce any disturbance of the tested material. Particularly, they do not use any probes which must be installed in the measure‐ ment site. Non-invasive methods include techniques such as airborne and satellite remote sensing (Jackson et al., 1996) or near infra-red reflectance spectroscopy (NIRS) (Cécillon et al., 2009). Remote techniques usually examine only the topsoil and require ground measure‐ ments for the proper calibration. However, they are irreplaceable for the monitoring of the

Non-destructive measurement methods have been adapted by agrophysics from various branches of science and industry. Therefore, the physical principles of those techniques vary greatly, from optical to electrical and nuclear methods. Despite the underlying measurement principle, the sensor device suitable for non-destructive and repetitive testing should pos‐ sess several universal features, such as a data-logging option, a power supply enabling longterm operation without recharging and the communication capability for the remote configuration and transferring of the measurement results to the user. An overview of vari‐ ous non-destructive soil water measurement methods is presented in Table 1. The measur‐ ing principle of each technique is briefly described, along with the most important

Because the determination of soil water status requires measurement of several parameters, the construction of integrated sensors, which measure several soil properties at the same time and on the same sample volume, becomes increasingly popular. For example, TDR and FDR methods enable the development of the soil water content and soil salinity measure‐ ment device, with the possibility of an addition of a temperature sensor (Skierucha et al.,

The traditional and standard water content measurement technique, called the thermogra‐ vimetric method, is based on a very simple concept of weighting a sample of a moist mate‐ rial, drying it and then weighting again. The difference between the mass of the moist and the dry material, equal to the mass of water evaporated from the original sample, divided by the mass of the dry material (assuming all of the water evaporated during the drying process), is an exact definition of mass water content on a dry basis (Equation 2). This quantity is also called gravimetric water content. Volumetric water content, when re‐ quired, may be then easily calculated from the mass water content, according to relations

However, the practical application of the thermogravimetric method is not so simple. First, a sample of a material under test needs to be collected. In case of soil testing, this process is invasive and disruptive to the soil profile and its surroundings. To achieve comparative re‐ sults, the process of drying needs to be standardised. The temperature and time length of the drying should be adjusted to the specifics of a given material. For soils, a sample is dried

soil properties on a global scale.

24 Advances in Agrophysical Research

advantages and limitations.

*2.2.1. Thermogravimetric method*

presented in section 1.1.

**2.2. Direct methods of water content measurement**

2006).

One of the most important chemical method of water content measurement is the Karl Fischer titration(Isengard, 2001). It is regarded as a reference method for determining the moisture content of food products.

In the volumetric variation of this technique, a sample of tested material, i.e. the analyte, is placed in a titration cell along with the working medium and the titrant solution. The chemi‐ cal components added to the analyte are: alcohol (ROH, usually methanol), sulphur dioxide (SO2), a base (B, usually imidazole) and iodine (I2). The overall reaction that occurs in the titration cell is as follows:

$$\rm{\rm{\tiny{3B}+ROH}+SO\_2} + \rm{I}\_2 + \rm{I}\_2\rm{O} \rightarrow \rm{\rm{3BH}^\*} + \rm{ROSO\_3^\*} + \rm{2I^\*} \tag{7}$$

In the net reaction, one mole of iodine is consumed per one mole of water from the analyte. The amount of water is therefore measured by the consumption of iodine. In the coulometric variation of this method, iodine is not added in the solution, but it is produced in the cell from iodide by anodic oxidation.

The end-point of the reaction is detected through electrochemical means. There are two plat‐ inum electrodes placed in the titration cell. In the so called bipotentiometric technique, a constant current is maintained on the electrodes and the voltage is monitored. In the biam‐ perometric variation, the voltage is kept constant and the current is measured. When all the water is consumed, the redox reactions between iodine and iodide ions occur, what causes an abrupt rise of current (biamperometric technique) or a sudden drop of voltage (bipoten‐ tiometric technique). The determination of the end-point of the reaction therefore allows for the calculation of the total amount of water in the sample. The end-point is usually amended by a stop delay time correction, accounting for water that is held by the sample and not im‐ mediately available for the reaction.

is naturally water. The thermalized neutrons are then detected by the probe. The number of counts of the slow neutrons is approximately proportional to the volumetric water content

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 27

With proper usage, this moisture content measurement method is very accurate. However, to test the water content of the top layer of the soil requires special precautions preventing escape of fast neutrons to the atmosphere. The main drawbacks of this technique are: the ra‐ diation hazard, expensive equipment, personnel training, low spatial resolution and the ne‐

Recently, a new remote sensing technique based on the scattering of the cosmic-ray neutrons has been proposed (Zreda et al., 2008). Cosmic rays, consisting mainly of protons, collide with atomic nuclei in atmosphere, creating cascades of secondary particles, including neu‐ trons. Those neutrons may then penetrate soil and scatter, the process of which depends on the soil water content, as described above. Some of these neutrons may diffuse back to the atmosphere, where they may be detected by remote sensors placed several metres above the ground. The measurement results are integrated over large areas (approx. 670 m in diame‐ ter), therefore they may be used as an intermediate between on site and satellite sensing (Dorigo et al., 2011). This moisture sensing technique is non-invasive and does not require usage of any radioactive or otherwise hazardous elements. Furthermore, it is suitable for

Dielectric properties or permittivity of agricultural products are of interest for several rea‐ sons. They include the sensing of moisture content in these products through its correlation with the dielectric properties of cereal grain and oilseed crops, the influence of permittivity on the dielectric heating of product at microwave or lower radio frequencies, and the poten‐ tial use of dielectric permittivity for sensing quality factors other than moisture content (Nel‐

The subject of interest for electromagnetic aquametry is analysing solids of different form and structure, as well as liquids containing water, for identification of their properties when placed in electromagnetic fields of radio and microwave frequencies (attenuation, reflection, phase angle, shift of resonant frequency, etc.). The physical principle of the dielectric mois‐ ture content measurement methods is based on the high value of relative dielectric permit‐ tivity of free water (about 80 at room temperature) with respect to air (equal to 1) and other

Microwave aquametry, as a branch of electromagnetic aquametry (Kraszewski, 2005) of ma‐ terials' dielectric properties, applies high measurement frequencies, where only dipole po‐ larization of free and bound water particles is active. The measurement techniques of microwave aquametry provide information about free water content. The following advan‐

**a.** contrary to lower frequencies, the conductivity effects on material properties can be ne‐

materials (for example, dry soil has relative dielectric permittivity of about 4 – 6).

tages of microwave aquametry were obvious since the early experiments:

in the soil.

cessity of the site specific calibration.

long-term environmental monitoring purposes.

*2.3.2. Dielectric methods – electromagnetic aquametry*

son, 2005; Skierucha et al., 2012).

glected,

The Karl Fischer titration is very accurate and can determine even extremely small amounts of water. However, the main disadvantage is that all the water in the sample should be made available for the reaction, which is sometimes difficult to achieve, for example in case of insoluble materials. This measurement method is also destructive, but fortunately it does not require large samples.

#### **2.3. Indirect methods of moisture content measurement**

Direct methods of moisture content determination in soils and biomaterials usually are time consuming, require laboratory equipment and are not practical for use in automatic systems to monitor environmental conditions and to control industrial technological processes. Due to spatial (from water volume fraction in soil micropores to water balance in continents) and temporal diversity (from milliseconds when analyzing water fluxes to days or weeks in weather prediction) of moisture content in analyzed objects, selectivity requirements and cost of the applied measurement equipment, the indirect methods of moisture content meas‐ urement require interdisciplinary approach that links deep knowledge about physical, chemical and biological processes in tested materials and engineering invention in designing appropriate sensors and meters.

The selection of moisture content measurement techniques presented below is not complete, it only covers representative or the most common ones.

#### *2.3.1. Neutron scattering*

One of the most accurate non-destructive water content measurement method involves de‐ tection of scattered neutrons emitted from a radioactive source placed within the soil (Hillel, 2004; Robinson et al., 2008). Although it requires installation of an access tube with the neu‐ tron source and the probe, which is invasive, the method allows for repetitive measure‐ ments of the site without further disturbances.

The neutron moisture meter commonly uses mixtures of radium and beryllium or americi‐ um and beryllium as the source of radiation. Radioactive elements emit into the soil gamma radiation and "fast neutrons", that is neutrons with high energy up to 15 MeV. The neutrons then collide with atomic nuclei present in the soil, scatter and lose energy, until they ap‐ proach a typical energy of particles at a given temperature, that is of about 0.03 eV. Neu‐ trons with such energy are called "thermalized" or "slow". Then they are finally absorbed by the atomic nuclei in soil. It happens that the neutrons are most effectively scattered through collisions with nuclei which mass is similar to their own, that is with protons, con‐ stituting the nuclei of hydrogen atoms. The most prevalent source of hydrogen atoms in soil is naturally water. The thermalized neutrons are then detected by the probe. The number of counts of the slow neutrons is approximately proportional to the volumetric water content in the soil.

With proper usage, this moisture content measurement method is very accurate. However, to test the water content of the top layer of the soil requires special precautions preventing escape of fast neutrons to the atmosphere. The main drawbacks of this technique are: the ra‐ diation hazard, expensive equipment, personnel training, low spatial resolution and the ne‐ cessity of the site specific calibration.

Recently, a new remote sensing technique based on the scattering of the cosmic-ray neutrons has been proposed (Zreda et al., 2008). Cosmic rays, consisting mainly of protons, collide with atomic nuclei in atmosphere, creating cascades of secondary particles, including neu‐ trons. Those neutrons may then penetrate soil and scatter, the process of which depends on the soil water content, as described above. Some of these neutrons may diffuse back to the atmosphere, where they may be detected by remote sensors placed several metres above the ground. The measurement results are integrated over large areas (approx. 670 m in diame‐ ter), therefore they may be used as an intermediate between on site and satellite sensing (Dorigo et al., 2011). This moisture sensing technique is non-invasive and does not require usage of any radioactive or otherwise hazardous elements. Furthermore, it is suitable for long-term environmental monitoring purposes.

#### *2.3.2. Dielectric methods – electromagnetic aquametry*

water is consumed, the redox reactions between iodine and iodide ions occur, what causes an abrupt rise of current (biamperometric technique) or a sudden drop of voltage (bipoten‐ tiometric technique). The determination of the end-point of the reaction therefore allows for the calculation of the total amount of water in the sample. The end-point is usually amended by a stop delay time correction, accounting for water that is held by the sample and not im‐

The Karl Fischer titration is very accurate and can determine even extremely small amounts of water. However, the main disadvantage is that all the water in the sample should be made available for the reaction, which is sometimes difficult to achieve, for example in case of insoluble materials. This measurement method is also destructive, but fortunately it does

Direct methods of moisture content determination in soils and biomaterials usually are time consuming, require laboratory equipment and are not practical for use in automatic systems to monitor environmental conditions and to control industrial technological processes. Due to spatial (from water volume fraction in soil micropores to water balance in continents) and temporal diversity (from milliseconds when analyzing water fluxes to days or weeks in weather prediction) of moisture content in analyzed objects, selectivity requirements and cost of the applied measurement equipment, the indirect methods of moisture content meas‐ urement require interdisciplinary approach that links deep knowledge about physical, chemical and biological processes in tested materials and engineering invention in designing

The selection of moisture content measurement techniques presented below is not complete,

One of the most accurate non-destructive water content measurement method involves de‐ tection of scattered neutrons emitted from a radioactive source placed within the soil (Hillel, 2004; Robinson et al., 2008). Although it requires installation of an access tube with the neu‐ tron source and the probe, which is invasive, the method allows for repetitive measure‐

The neutron moisture meter commonly uses mixtures of radium and beryllium or americi‐ um and beryllium as the source of radiation. Radioactive elements emit into the soil gamma radiation and "fast neutrons", that is neutrons with high energy up to 15 MeV. The neutrons then collide with atomic nuclei present in the soil, scatter and lose energy, until they ap‐ proach a typical energy of particles at a given temperature, that is of about 0.03 eV. Neu‐ trons with such energy are called "thermalized" or "slow". Then they are finally absorbed by the atomic nuclei in soil. It happens that the neutrons are most effectively scattered through collisions with nuclei which mass is similar to their own, that is with protons, con‐ stituting the nuclei of hydrogen atoms. The most prevalent source of hydrogen atoms in soil

mediately available for the reaction.

**2.3. Indirect methods of moisture content measurement**

it only covers representative or the most common ones.

ments of the site without further disturbances.

not require large samples.

26 Advances in Agrophysical Research

appropriate sensors and meters.

*2.3.1. Neutron scattering*

Dielectric properties or permittivity of agricultural products are of interest for several rea‐ sons. They include the sensing of moisture content in these products through its correlation with the dielectric properties of cereal grain and oilseed crops, the influence of permittivity on the dielectric heating of product at microwave or lower radio frequencies, and the poten‐ tial use of dielectric permittivity for sensing quality factors other than moisture content (Nel‐ son, 2005; Skierucha et al., 2012).

The subject of interest for electromagnetic aquametry is analysing solids of different form and structure, as well as liquids containing water, for identification of their properties when placed in electromagnetic fields of radio and microwave frequencies (attenuation, reflection, phase angle, shift of resonant frequency, etc.). The physical principle of the dielectric mois‐ ture content measurement methods is based on the high value of relative dielectric permit‐ tivity of free water (about 80 at room temperature) with respect to air (equal to 1) and other materials (for example, dry soil has relative dielectric permittivity of about 4 – 6).

Microwave aquametry, as a branch of electromagnetic aquametry (Kraszewski, 2005) of ma‐ terials' dielectric properties, applies high measurement frequencies, where only dipole po‐ larization of free and bound water particles is active. The measurement techniques of microwave aquametry provide information about free water content. The following advan‐ tages of microwave aquametry were obvious since the early experiments:

**a.** contrary to lower frequencies, the conductivity effects on material properties can be ne‐ glected,

**b.** penetration depth is much larger than that of infrared radiation and permits the prob‐ ing of a significant volume of material being transported on a conveyor or in a pipe,

the surfaces between different materials, from which the cell is formed (Markx and Davey, 1999). The α-dispersion is due to the tangential flow of ions across cell surfaces, the β-dis‐ persion results from the build-up of charge at cell membranes due to the Maxwell–Wagner effect, the δ-dispersion is produced by the rotation of macromolecular side-chains and bound water, and the γ-dispersion is due to the dipolar rotation of small molecules, particu‐ larly water. The low frequency polarization masks the bound water and free water disper‐ sion effects. Therefore, the use of microwaves in the analysis of electromagnetic field

The most common dielectric techniques for determination of moisture content in soils and biomaterials use capacitance sensors. They usually work in low frequencies up to 150 MHz. A sensor is in a form of a capacitor of parameters modified by dielectric permittivity and electrical conductivity of the surrounding material. The representative probes applied for the measurement of soil moisture and electrical conductivity are: Theta Probe or ECHO moisture sensor with performance and characteristics described broadly in literature (Li et al., 2005; Kizito et al., 2008). Capacitance sensors are not expensive and when equipped with wireless communication and scattered on large areas, they are especially useful in monitor‐ ing soil moisture for environmental and irrigation scheduling (Zhang et al., 2011), although

Radio frequency and microwaves techniques include: reflection measurements with the use of an open-ended coaxial probe (Skierucha et al., 2004; Agilent, 2006), transmission measure‐ ments with the use of materials' samples placed inside transmission lines and microwave

The complex relative permittivity *ε \** of a material can be expressed in the following complex

poles rotation,*<sup>σ</sup>* (S <sup>m</sup>-1) is the ionic conductivity, *<sup>ω</sup>* (rad <sup>s</sup>-1) is the angular frequency and *ε*0 is the permittivity of free space or vacuum (8.854 10-12 F m-1), and *j* = -1. Mechanisms that con‐ tribute to the dielectric loss in heterogeneous mixtures include polar, electronic, atomic and Maxwell–Wagner responses. Aquametry measurements at RF and microwave frequencies are of practical importance and they are currently used for applications in food processing (Venkatesh and Raghavan, 2004), food treatment (Marra et al., 2009) and quality determina‐

<sup>+</sup> *<sup>σ</sup>*

is referred to as the dielectric constantand represents stored energy when

''

*<sup>ε</sup>*0*<sup>ω</sup>* ) (8)

stands for the contribution due to di‐

, which is the imaginary

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 29

interactions with soils and biomaterials is recommended.

they are not so accurate as TDR sensors (Evett et al., 2012).

*ε* \* =*ε* ' - *jε* '' =*ε* ' - *j*(*ε<sup>d</sup>* ''

part, influences energy absorption and attenuation, *ε<sup>d</sup>*

the material is exposed to anelectric field, while the loss factor *ε ''*

tion of biomaterials and food products (Wang, 2003; Sosa-Morales et al., 2010).

*2.3.2.1. Frequency domain sensors*

resonators (King, 2000).

form:

The real part *ε '*


Since heterogeneous systems have interfaces where the materials of different electrical prop‐ erties contact each other, producing interfacial polarization that is due to the build-up of charge on the interfaces and causing current flow. Through introduction of external electri‐ cal field of variable frequency, it is possible to observe changes of the complex dielectric per‐ mittivity of the examined heterogenic material (electrical dispersion). The real part of the permittivity describes the ability of the material to polarize the internal electrical dipoles and charge carriers, and its imaginary part describes the energy loss of the electric field (die‐ lectric loss and conductivity loss). These changes are characteristic for each analysed materi‐ al because of its unique physical and chemical properties. The dielectric relaxation due to interfacial polarization provides information on the heterogeneous structure and the electri‐ cal properties of the constituent components.

**Figure 1.** Idealized spectrum of the real part of the complex dielectric permittivity of cell suspensions and tissues. The step changes in dielectric permittivity are called dispersions and are due to the loss of particular polarization processes as frequency increases (from (Markx and Davey, 1999))

For most substances the electrical permittivity and conductivity are constant only for a limit‐ ed range of frequencies. Within increasing frequency permittivity decreases, while the con‐ ductivity increases abruptly. These abrupt changes are called dispersions, and each of them represents a specific process of polarization. Biological materials are characterized by high dispersion, especially at low frequencies (Figure 1). It is caused by interfacial polarization on the surfaces between different materials, from which the cell is formed (Markx and Davey, 1999). The α-dispersion is due to the tangential flow of ions across cell surfaces, the β-dis‐ persion results from the build-up of charge at cell membranes due to the Maxwell–Wagner effect, the δ-dispersion is produced by the rotation of macromolecular side-chains and bound water, and the γ-dispersion is due to the dipolar rotation of small molecules, particu‐ larly water. The low frequency polarization masks the bound water and free water disper‐ sion effects. Therefore, the use of microwaves in the analysis of electromagnetic field interactions with soils and biomaterials is recommended.

#### *2.3.2.1. Frequency domain sensors*

**b.** penetration depth is much larger than that of infrared radiation and permits the prob‐ ing of a significant volume of material being transported on a conveyor or in a pipe, **c.** physical contact between the equipment and the material under test is not required, al‐

**d.** in contrast to infrared radiation, it is relatively insensitive to environmental conditions, thus dust and water vapour in industrial facilities do not affect the measurement, **e.** water reacts specifically with certain frequencies in the microwave region (relaxation)

**f.** contrary to chemical methods, it does not alter or contaminate the test material, thus the

Since heterogeneous systems have interfaces where the materials of different electrical prop‐ erties contact each other, producing interfacial polarization that is due to the build-up of charge on the interfaces and causing current flow. Through introduction of external electri‐ cal field of variable frequency, it is possible to observe changes of the complex dielectric per‐ mittivity of the examined heterogenic material (electrical dispersion). The real part of the permittivity describes the ability of the material to polarize the internal electrical dipoles and charge carriers, and its imaginary part describes the energy loss of the electric field (die‐ lectric loss and conductivity loss). These changes are characteristic for each analysed materi‐ al because of its unique physical and chemical properties. The dielectric relaxation due to interfacial polarization provides information on the heterogeneous structure and the electri‐

**Figure 1.** Idealized spectrum of the real part of the complex dielectric permittivity of cell suspensions and tissues. The step changes in dielectric permittivity are called dispersions and are due to the loss of particular polarization processes

For most substances the electrical permittivity and conductivity are constant only for a limit‐ ed range of frequencies. Within increasing frequency permittivity decreases, while the con‐ ductivity increases abruptly. These abrupt changes are called dispersions, and each of them represents a specific process of polarization. Biological materials are characterized by high dispersion, especially at low frequencies (Figure 1). It is caused by interfacial polarization on

lowing on-line continuous and remote moisture sensing,

allowing even small amounts of water to be detected.

measurement is non-destructive.

28 Advances in Agrophysical Research

cal properties of the constituent components.

as frequency increases (from (Markx and Davey, 1999))

The most common dielectric techniques for determination of moisture content in soils and biomaterials use capacitance sensors. They usually work in low frequencies up to 150 MHz. A sensor is in a form of a capacitor of parameters modified by dielectric permittivity and electrical conductivity of the surrounding material. The representative probes applied for the measurement of soil moisture and electrical conductivity are: Theta Probe or ECHO moisture sensor with performance and characteristics described broadly in literature (Li et al., 2005; Kizito et al., 2008). Capacitance sensors are not expensive and when equipped with wireless communication and scattered on large areas, they are especially useful in monitor‐ ing soil moisture for environmental and irrigation scheduling (Zhang et al., 2011), although they are not so accurate as TDR sensors (Evett et al., 2012).

Radio frequency and microwaves techniques include: reflection measurements with the use of an open-ended coaxial probe (Skierucha et al., 2004; Agilent, 2006), transmission measure‐ ments with the use of materials' samples placed inside transmission lines and microwave resonators (King, 2000).

The complex relative permittivity *ε \** of a material can be expressed in the following complex form:

$$
\varepsilon^\* = \varepsilon^\circ \text{ - } j\varepsilon^\circ = \varepsilon^\circ \text{ - } j\left(\varepsilon\_d^\circ + \frac{\sigma}{\varepsilon\_0 \omega}\right) \tag{8}
$$

The real part *ε '* is referred to as the dielectric constantand represents stored energy when the material is exposed to anelectric field, while the loss factor *ε ''* , which is the imaginary part, influences energy absorption and attenuation, *ε<sup>d</sup>* '' stands for the contribution due to di‐ poles rotation,*<sup>σ</sup>* (S <sup>m</sup>-1) is the ionic conductivity, *<sup>ω</sup>* (rad <sup>s</sup>-1) is the angular frequency and *ε*0 is the permittivity of free space or vacuum (8.854 10-12 F m-1), and *j* = -1. Mechanisms that con‐ tribute to the dielectric loss in heterogeneous mixtures include polar, electronic, atomic and Maxwell–Wagner responses. Aquametry measurements at RF and microwave frequencies are of practical importance and they are currently used for applications in food processing (Venkatesh and Raghavan, 2004), food treatment (Marra et al., 2009) and quality determina‐ tion of biomaterials and food products (Wang, 2003; Sosa-Morales et al., 2010).

#### *2.3.2.2. TDR technique*

Time domain reflectometry (TDR) is a fast, accurate, and safe technique. The basic principle of time domain reflectometry (TDR) is the same as in radars. The system sends an electro‐ magnetic pulse along the waveguide, which reflects on the mismatch impedance. This tech‐ nique assumes that the material is homogeneous in the vicinity of the waveguide forming a TDR sensor.

*<sup>v</sup>* <sup>≈</sup> *<sup>c</sup>*

*ECb* <sup>≈</sup> *<sup>ε</sup>*(*θv*)

the length of TDR probe rods inserted into the soil.

apparent) electrical conductivity, *ECb* (S <sup>m</sup>-1

free water, solid phase and air.

*2.3.3. Material specific calibration*

nisms in the process being examined.

ton, 1985)

*<sup>ε</sup>*(*θv*) <sup>=</sup> *<sup>c</sup>*

*<sup>n</sup>* <sup>=</sup> <sup>2</sup>*<sup>L</sup>*

where *c* is a velocity of light in free space, *ε*(*θv*) is the real part of the complex dielectric per‐ mittivity dependent on its volumetric water content, *n* is the medium refractive index; *L* is

Also, the amplitude of the pulse at the point (b) decreases with the increase of soil bulk (or

<sup>120</sup>*π<sup>L</sup>* ln( *Uin*

where *Uin* and *Uout* are the amplitude of the pulse before and after attenuation caused by the pulse travel twice a distance of the probe length, *L*. The value of *ECb* is a strong indicator of the ionic concentration in soils, i.e. its salinity (Malicki and Walczak, 1999; Friedman, 2005). The TDR determined dielectric constant can be utilized to determine the volumetric water content, *θv*, on the base of empirical calibration (Topp et al., 1980; Malicki and Skieru‐ cha, 1989; Malicki et al., 1996) or theoretical models (Roth et al., 1990; Or and Wraith, 1999) of the sensor in the multiphase medium that includes the fraction of bound water beside

TDR sensors are more precise than capacitance sensors due to higher frequency range of work (about 1 GHz) (Robinson et al., 2008), which minimizes the influence of salinity of the tested material. Although the calibration equations *θv*(*εb*), such as Equation (11), are univer‐ sal for majority of mineral soils giving the mean measurement accuracy ±2% of the meas‐ ured value of *θv*, the presence of bound water (in materials of large specific surface area, like clay) and variable density of tested material can significantly increase the TDR determined volume fraction of water. Accounting for these effects, the decrease of the moisture meas‐

Moisture content of porous materials is difficult to monitor accurately because of the hetero‐ geneity of pore space, bulk density and structure. There are several types of commercial moisture probes available, including those that employ time domain reflectometry and fre‐ quency domain reflectometry, calibrated in the field or laboratory conditions. However, while a moisture sensor performance can be expressed in the sense of measurement accura‐ cy, predicting the final accuracy in terms of moisture content dramatically depends on the properties of the material to be monitored and the particular physical and chemical mecha‐

urement error by TDR technique requires material specific calibrations.

*Uout*

<sup>∆</sup> *<sup>t</sup>* (9)

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 31

), according to Equation (10) (Dasberg and Dal‐

) (10)

The TDR probe consists of two waveguides connected together: a coaxial one, called the feeder, and a parallel one, called the sensor, made of two or three parallel metal rods insert‐ ed into the measured medium (Figure 2).

**Figure 2.** Hardware setup for simultaneous measurement of soil water content and electrical conductivity using Time Domain Reflectometry method, from (Skierucha and Malicki, 2004)

The initial needle pulse or step pulse travels from the generator by the feeder towards the sensor. The recorder registers this pulse as it passes a T-connector. There is a rapid change in geometry of the electromagnetic wave travel path between the feeder and the sensor. At this point, some energy of the pulse is reflected back to the generator, and the remaining pulse is traveling along the parallel waveguide to be reflected completely from the rods ending. The successive reflections are recorded for calculation of the time distance between the two re‐ flections (a) and (b). Three reflectograms (voltage as a function of time at a chosen point in the feeder) are presented in Figure 2. They represent cases when the sensor was placed in dry, wet and water saturated soil. The time distance, Δ*t*, necessary for the pulse to cover the distance equal to the double length of metal rods in the measured medium, increases with the soil dielectric constant, thus with water content. The reason for that is the change of elec‐ tromagnetic propagation velocity *v*in media of different dielectric constants, according to Equation (9)

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 31

$$
\psi v \approx \frac{c}{\sqrt{\epsilon(\theta\_v)}} = \frac{c}{n} = \frac{2L}{\Delta t} \tag{9}
$$

where *c* is a velocity of light in free space, *ε*(*θv*) is the real part of the complex dielectric per‐ mittivity dependent on its volumetric water content, *n* is the medium refractive index; *L* is the length of TDR probe rods inserted into the soil.

Also, the amplitude of the pulse at the point (b) decreases with the increase of soil bulk (or apparent) electrical conductivity, *ECb* (S <sup>m</sup>-1 ), according to Equation (10) (Dasberg and Dal‐ ton, 1985)

$$EC\_b \approx \frac{\sqrt{\varepsilon(\theta\_v)}}{120\pi L} \ln\left(\frac{\mathcal{U}\_{in}}{\mathcal{U}\_{out}}\right) \tag{10}$$

where *Uin* and *Uout* are the amplitude of the pulse before and after attenuation caused by the pulse travel twice a distance of the probe length, *L*. The value of *ECb* is a strong indicator of the ionic concentration in soils, i.e. its salinity (Malicki and Walczak, 1999; Friedman, 2005). The TDR determined dielectric constant can be utilized to determine the volumetric water content, *θv*, on the base of empirical calibration (Topp et al., 1980; Malicki and Skieru‐ cha, 1989; Malicki et al., 1996) or theoretical models (Roth et al., 1990; Or and Wraith, 1999) of the sensor in the multiphase medium that includes the fraction of bound water beside free water, solid phase and air.

TDR sensors are more precise than capacitance sensors due to higher frequency range of work (about 1 GHz) (Robinson et al., 2008), which minimizes the influence of salinity of the tested material. Although the calibration equations *θv*(*εb*), such as Equation (11), are univer‐ sal for majority of mineral soils giving the mean measurement accuracy ±2% of the meas‐ ured value of *θv*, the presence of bound water (in materials of large specific surface area, like clay) and variable density of tested material can significantly increase the TDR determined volume fraction of water. Accounting for these effects, the decrease of the moisture meas‐ urement error by TDR technique requires material specific calibrations.

#### *2.3.3. Material specific calibration*

*2.3.2.2. TDR technique*

30 Advances in Agrophysical Research

ed into the measured medium (Figure 2).

Domain Reflectometry method, from (Skierucha and Malicki, 2004)

TDR sensor.

Equation (9)

Time domain reflectometry (TDR) is a fast, accurate, and safe technique. The basic principle of time domain reflectometry (TDR) is the same as in radars. The system sends an electro‐ magnetic pulse along the waveguide, which reflects on the mismatch impedance. This tech‐ nique assumes that the material is homogeneous in the vicinity of the waveguide forming a

The TDR probe consists of two waveguides connected together: a coaxial one, called the feeder, and a parallel one, called the sensor, made of two or three parallel metal rods insert‐

**Figure 2.** Hardware setup for simultaneous measurement of soil water content and electrical conductivity using Time

The initial needle pulse or step pulse travels from the generator by the feeder towards the sensor. The recorder registers this pulse as it passes a T-connector. There is a rapid change in geometry of the electromagnetic wave travel path between the feeder and the sensor. At this point, some energy of the pulse is reflected back to the generator, and the remaining pulse is traveling along the parallel waveguide to be reflected completely from the rods ending. The successive reflections are recorded for calculation of the time distance between the two re‐ flections (a) and (b). Three reflectograms (voltage as a function of time at a chosen point in the feeder) are presented in Figure 2. They represent cases when the sensor was placed in dry, wet and water saturated soil. The time distance, Δ*t*, necessary for the pulse to cover the distance equal to the double length of metal rods in the measured medium, increases with the soil dielectric constant, thus with water content. The reason for that is the change of elec‐ tromagnetic propagation velocity *v*in media of different dielectric constants, according to

Moisture content of porous materials is difficult to monitor accurately because of the hetero‐ geneity of pore space, bulk density and structure. There are several types of commercial moisture probes available, including those that employ time domain reflectometry and fre‐ quency domain reflectometry, calibrated in the field or laboratory conditions. However, while a moisture sensor performance can be expressed in the sense of measurement accura‐ cy, predicting the final accuracy in terms of moisture content dramatically depends on the properties of the material to be monitored and the particular physical and chemical mecha‐ nisms in the process being examined.

The reference values used for calibration in the moisture content measurement of porous materials are the ones taken from thermogravimetric method described in part 2.2.

Calibration equation relating the dielectric constant to the soil moisture content are necessa‐ ry. The *θv*(*εb*) equation generally is provided by a manufacturer. However, in some cases site-specific calibration may be needed. For example, field calibration may be necessary in fine-textured soils.

Time domain reflectometry (TDR) is becoming a widely used method to determine volumet‐ ric soil water content, *θv*, from measured apparent (effective, bulk) relative dielectric con‐ stant (permittivity), *εb*, using the empirical Topp-Davis-Annan (Topp et al., 1980) calibration equation:

$$
\theta\_v = -5.3 \times 10^{-2} + 2.92 \times 10^{-2} \varepsilon\_b - 5.5 \times 10^{-4} \varepsilon\_b^2 + 4.3 \times 10^{-6} \varepsilon\_b^3 \tag{11}
$$

reached and the suction inside the tensiometer equals the soil matric potential. When the soil is wetted, flow may occur in the reverse direction, i.e., soil water enters the tensiometer

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 33

According to equation (6), under equilibrium conditions the material's water potential is equal to the potential of water vapor in the surrounding air, which is measured by a psy‐ chrometers. A special construction of a psychrometer, called a thermocouple or Peltier psy‐ chrometer, has been developed to be used for applications in soil and biomaterials for the measurement of the sum of matric and osmotic potentials. The construction of a typical ther‐ mocouple psychrometers sensor and its connection to a readout device as well as a sample

**Figure 3.** a) Peltier psychrometer sensor with porous ceramic thermocouple shield (Andraski and Scanlon, 2002) and the meter connector with installed electronics for cold junction compensation and storage of the sensor individual

The measurement cycle consists of steps that are controlled by the microcontroller and elec‐ tronic circuitry of the meter. These steps may vary according to the water potential to be measured, temperature, required accuracy and time interval of measurements. Optimization of measurement process with respect to different restrictions may lead to various measure‐ ment procedures. The measurement sequence taking place to determine psychrometric wa‐

**1.** The constantan/chromel thermocouple should not have water condensed on the fine wires. This is assured by passing the warming current of an appropriate value through the junction and then, after stopping the current, the junction should attain the tempera‐ ture equilibrium with the air space surrounding it. Also the air space must be in the

**2.** The Peltier cooling current is passing through the constantan/chromel thermocouple junction. The magnitude and duration of cooling current must be sufficient to cool the junction below the dew point temperature of the equilibrated air. When the tempera‐

temperature and vapor equilibrium with the measured sample.

measurement device output are presented in Figure 3a (Skierucha, 2005).

parameters; b) recorded output of the thermocouple psychrometer

ter potential value is as follows:

until a new equilibrium is attained.

*2.4.2. Thermocouple psychrometry*

Dirksen et al. (Dirksen and Dasberg, 1993) showed that this equation is not adequate for all soils. Other studies showed that bulk density, and thus also porosity, substantially affects the relation between dielectric constant and water content. Two equivalent, empirical, nor‐ malized conversion functions were found (Malicki et al., 1996), one accounting for soil bulk density and the other for soil porosity. Each of them reduced the root mean square error of the dielectric TDR determinations of moisture to 0.03, regardless of the materials bulk densi‐ ty and porosity.

#### **2.4. Water potential**

Total water potential in a material (e.g. soil), described by Equation (6), depends on several elements, two of which are of the most practical importance: matric potential *ϕm* and osmot‐ ic potential *ϕo*. The relation between volumetric water content and water potential of the soil is called soil-water characteristic curve. Its shape differs for clay, silt and sandy soil, as water retention characteristics differ for these soils. Knowing soil water characteristic curve and water potential value, one can calculate water content in this material. The typical measure‐ ment methods of water potential of soils and biomaterials use tensiometers and psychrome‐ ters as the sensing elements.

#### *2.4.1. Tensiometry*

A tensiometer is a device that measures how hard the plant is working to extract water from the soil. It directly measures the physical force that the root system must overcome in order to access water held in the soil (also known as matric potential *ϕm*). It is built from sealed water-filled tube, equipped with a porous tip installed in the ground to the desired root zone (Or and Wraith, 2002). When the matric potential of the soil is lower (more negative) than the equivalent pressure inside the tensiometer cup, water moves from the tensiometer along a potential energy gradient to the soil through the saturated porous cup, thereby cre‐ ating suction sensed by the gauge. Water flow into the soil continues until equilibrium is reached and the suction inside the tensiometer equals the soil matric potential. When the soil is wetted, flow may occur in the reverse direction, i.e., soil water enters the tensiometer until a new equilibrium is attained.

### *2.4.2. Thermocouple psychrometry*

The reference values used for calibration in the moisture content measurement of porous

Calibration equation relating the dielectric constant to the soil moisture content are necessa‐ ry. The *θv*(*εb*) equation generally is provided by a manufacturer. However, in some cases site-specific calibration may be needed. For example, field calibration may be necessary in

Time domain reflectometry (TDR) is becoming a widely used method to determine volumet‐ ric soil water content, *θv*, from measured apparent (effective, bulk) relative dielectric con‐ stant (permittivity), *εb*, using the empirical Topp-Davis-Annan (Topp et al., 1980) calibration

*<sup>ε</sup><sup>b</sup>* - 5.5×10-4

Dirksen et al. (Dirksen and Dasberg, 1993) showed that this equation is not adequate for all soils. Other studies showed that bulk density, and thus also porosity, substantially affects the relation between dielectric constant and water content. Two equivalent, empirical, nor‐ malized conversion functions were found (Malicki et al., 1996), one accounting for soil bulk density and the other for soil porosity. Each of them reduced the root mean square error of the dielectric TDR determinations of moisture to 0.03, regardless of the materials bulk densi‐

Total water potential in a material (e.g. soil), described by Equation (6), depends on several elements, two of which are of the most practical importance: matric potential *ϕm* and osmot‐ ic potential *ϕo*. The relation between volumetric water content and water potential of the soil is called soil-water characteristic curve. Its shape differs for clay, silt and sandy soil, as water retention characteristics differ for these soils. Knowing soil water characteristic curve and water potential value, one can calculate water content in this material. The typical measure‐ ment methods of water potential of soils and biomaterials use tensiometers and psychrome‐

A tensiometer is a device that measures how hard the plant is working to extract water from the soil. It directly measures the physical force that the root system must overcome in order to access water held in the soil (also known as matric potential *ϕm*). It is built from sealed water-filled tube, equipped with a porous tip installed in the ground to the desired root zone (Or and Wraith, 2002). When the matric potential of the soil is lower (more negative) than the equivalent pressure inside the tensiometer cup, water moves from the tensiometer along a potential energy gradient to the soil through the saturated porous cup, thereby cre‐ ating suction sensed by the gauge. Water flow into the soil continues until equilibrium is

*εb*

<sup>2</sup> + 4.3×10-6

*εb*

<sup>3</sup> (11)

materials are the ones taken from thermogravimetric method described in part 2.2.

*<sup>θ</sup><sup>v</sup>* <sup>=</sup> - 5.3×10-2 <sup>+</sup> 2.92×10-2

fine-textured soils.

32 Advances in Agrophysical Research

equation:

ty and porosity.

**2.4. Water potential**

ters as the sensing elements.

*2.4.1. Tensiometry*

According to equation (6), under equilibrium conditions the material's water potential is equal to the potential of water vapor in the surrounding air, which is measured by a psy‐ chrometers. A special construction of a psychrometer, called a thermocouple or Peltier psy‐ chrometer, has been developed to be used for applications in soil and biomaterials for the measurement of the sum of matric and osmotic potentials. The construction of a typical ther‐ mocouple psychrometers sensor and its connection to a readout device as well as a sample measurement device output are presented in Figure 3a (Skierucha, 2005).

**Figure 3.** a) Peltier psychrometer sensor with porous ceramic thermocouple shield (Andraski and Scanlon, 2002) and the meter connector with installed electronics for cold junction compensation and storage of the sensor individual parameters; b) recorded output of the thermocouple psychrometer

The measurement cycle consists of steps that are controlled by the microcontroller and elec‐ tronic circuitry of the meter. These steps may vary according to the water potential to be measured, temperature, required accuracy and time interval of measurements. Optimization of measurement process with respect to different restrictions may lead to various measure‐ ment procedures. The measurement sequence taking place to determine psychrometric wa‐ ter potential value is as follows:


ture of the junction is below the dew point, water condenses on the junction from the surrounding air. The Peltier current is discontinued and the thermocouple output volt‐ age starts to be monitored (Figure 3b, point A). During the evaporation of water con‐ densed on the thermocouple junction, its temperature does not change rapidly (points A and B in Figure 3b). This temperature — the wet bulb depression temperature, de‐ pends on relative humidity of the air surrounding the sensor. The wet bulb depression lasts until all water evaporates from the junction and the thermocouple temperature re‐ turns to the ambient (points B and C in Figure 3b).

the equilibrium in water tension between the soil and the block. Therefore, this method may

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 35

Thermal properties of a material may also be used to determine its water content. Soil volu‐ metric heat capacity (in units J m-3 K-1), defined as the amount of energy needed to increase the temperature of a unit volume of soil by a degree, depends on volumetric water content, as well as other factors such as porosity and heat capacity of the solid phase. If those addi‐ tional quantities are known, soil water content may be calculated from the calorimetric measurements of soil heat capacity. Soil thermal conductivity, defined as the ability to con‐ duct heat (in units W m-1 K-1), depends on the moisture as well. A guarded hot-plate meth‐ od, in which the sample is placed between the heating and cooling plates and its thermal conductivity is measured, may therefore be used as a water content determination technique

A gamma-ray absorption moisture meter has also been developed, which possesses better spatial resolution than a neutron moisture meter. It consists of a gamma-ray source unit placed in the soil, usually containing radioactive caesium, and a detector, placed in the soil at some distance from the source. The amount of radiation detected by the probe depends on the attenuation coefficient and the distance from the source. It happens that the absorp‐ tion of the gamma radiation by the soil depends on the moisture content. This method, ap‐ plicable mostly in laboratory conditions, is cumbersome, presents radiation hazard and

Other techniques of moisture measurement, applicable mostly to food products and agricul‐ tural materials, include direct methods such as infrared, halogen and microwave drying (similar in principle to oven drying, or thermogravimetric method for soils), desiccation by water transfer, distillation, chemical methods based on calcium carbide or calcium hydride reactions with water, methods combining evaporation with Karl Fischer titration or diphos‐ phorus pentoxide method (Isengard, 2001). Among the indirect water detection techniques are optical methods such as polarimetry and refractometry, and near infrared (NIR) techni‐ que. Other parts of the electromagnetic spectrum are utilised by a low-resolution nuclear magnetic resonance (NMR) technique (based on the influence of a radio frequency pulse on a nuclear spin of hydrogen nuclei placed in a constant magnetic field) or a microwave cavity

resonator method. The methods listed above require product-specific calibrations.

The appearance of large information banks on soil properties in Europe (Great Britain, France, Holland, Denmark etc.) was provoked by necessity of increasing of agricultural production economics, i.e. the commercial price of soil as the production medium. Protec‐ tion of soil as element of natural environment was the reason of initiating in 1980 year of national program of soil mapping in Norway. The projects of soil monitoring were limit‐

**3. Aquametry applications in agrophysics**

be actually better suited for measurements of water potential than the water content.

(Robinson et al., 2008).

therefore is not very popular.

**3.1. Soil quality**

For soils, water potential measurements in field condition cannot be acceptably performed by one method in the full range of variability, i.e. from 0 MPa to the wilting point water po‐ tential –1.5 MPa, and below. Tensiometers work from 0 to about –0.09 MPa and respond on‐ ly to soil matrix potential. Porous gypsum blocks are available in the full range of interest but they respond also to soil salinity and therefore need site-specific calibration. Psychro‐ metric sensors seem to be the ideal solution because they measure the humidity of air that remains in equilibrium with a sample of material containing moisture and they respond to total soil water potential. However in contrary to tensiometers, they work in the range from about –0.3 to –6 MPa. Therefore, there is no reliable sensor covering the range of soil water potential from –0.09 to –0.3 MPa in the field conditions. The thermocouple psychrometry is reliable method of water potential measurement (Savage and Cass, 1984; Andraski and Scanlon, 2002), provided that proper precautions are applied to sensors. This include careful cleaning, handling and calibration of the sensors that are susceptible to acid environment. Special attention should be paid to eliminate the temperature gradients in the sensor during measurements. The current state of the thermocouple psychrometry is presented in (An‐ draski and Scanlon, 2002).The respective sensors are commercially available but the com‐ plexity of measurements and rigid temperature conditions forced on the measurement process make this method not convenient.

#### **2.5. Other methods of water content measurement**

There is a number of other moisture measurement methods based on several different phys‐ ical principles (Hillel, 2004; Robinson et al., 2008; Vereecken et al., 2008).

One of the earliest method of soil moisture measurement, proposed at the end of the 19th century, bases on soil electrical conductivity. However, the electrical conductivity of soil de‐ pends not only on water content, but also on soil salinity, texture, composition and tempera‐ ture (Robinson et al., 2008). On the other hand, when moisture content is known, soil electrical conductivity may be effectively used as a salinity measure. Despite this selectivity issue, soil moisture sensor devices, based on the electrical resistance measurements, are be‐ ing used to evaluate the status of water in the soil.

Electrical resistance blocks are porous bodies comprising of gypsum, nylon or fiberglass, and containing two electrodes, may be used to evaluate soil moisture by measuring electri‐ cal resistance of soil water filling the pores. The soil water fills the pores in order to achieve the equilibrium in water tension between the soil and the block. Therefore, this method may be actually better suited for measurements of water potential than the water content.

Thermal properties of a material may also be used to determine its water content. Soil volu‐ metric heat capacity (in units J m-3 K-1), defined as the amount of energy needed to increase the temperature of a unit volume of soil by a degree, depends on volumetric water content, as well as other factors such as porosity and heat capacity of the solid phase. If those addi‐ tional quantities are known, soil water content may be calculated from the calorimetric measurements of soil heat capacity. Soil thermal conductivity, defined as the ability to con‐ duct heat (in units W m-1 K-1), depends on the moisture as well. A guarded hot-plate meth‐ od, in which the sample is placed between the heating and cooling plates and its thermal conductivity is measured, may therefore be used as a water content determination technique (Robinson et al., 2008).

A gamma-ray absorption moisture meter has also been developed, which possesses better spatial resolution than a neutron moisture meter. It consists of a gamma-ray source unit placed in the soil, usually containing radioactive caesium, and a detector, placed in the soil at some distance from the source. The amount of radiation detected by the probe depends on the attenuation coefficient and the distance from the source. It happens that the absorp‐ tion of the gamma radiation by the soil depends on the moisture content. This method, ap‐ plicable mostly in laboratory conditions, is cumbersome, presents radiation hazard and therefore is not very popular.

Other techniques of moisture measurement, applicable mostly to food products and agricul‐ tural materials, include direct methods such as infrared, halogen and microwave drying (similar in principle to oven drying, or thermogravimetric method for soils), desiccation by water transfer, distillation, chemical methods based on calcium carbide or calcium hydride reactions with water, methods combining evaporation with Karl Fischer titration or diphos‐ phorus pentoxide method (Isengard, 2001). Among the indirect water detection techniques are optical methods such as polarimetry and refractometry, and near infrared (NIR) techni‐ que. Other parts of the electromagnetic spectrum are utilised by a low-resolution nuclear magnetic resonance (NMR) technique (based on the influence of a radio frequency pulse on a nuclear spin of hydrogen nuclei placed in a constant magnetic field) or a microwave cavity resonator method. The methods listed above require product-specific calibrations.

## **3. Aquametry applications in agrophysics**

#### **3.1. Soil quality**

ture of the junction is below the dew point, water condenses on the junction from the surrounding air. The Peltier current is discontinued and the thermocouple output volt‐ age starts to be monitored (Figure 3b, point A). During the evaporation of water con‐ densed on the thermocouple junction, its temperature does not change rapidly (points A and B in Figure 3b). This temperature — the wet bulb depression temperature, de‐ pends on relative humidity of the air surrounding the sensor. The wet bulb depression lasts until all water evaporates from the junction and the thermocouple temperature re‐

For soils, water potential measurements in field condition cannot be acceptably performed by one method in the full range of variability, i.e. from 0 MPa to the wilting point water po‐ tential –1.5 MPa, and below. Tensiometers work from 0 to about –0.09 MPa and respond on‐ ly to soil matrix potential. Porous gypsum blocks are available in the full range of interest but they respond also to soil salinity and therefore need site-specific calibration. Psychro‐ metric sensors seem to be the ideal solution because they measure the humidity of air that remains in equilibrium with a sample of material containing moisture and they respond to total soil water potential. However in contrary to tensiometers, they work in the range from about –0.3 to –6 MPa. Therefore, there is no reliable sensor covering the range of soil water potential from –0.09 to –0.3 MPa in the field conditions. The thermocouple psychrometry is reliable method of water potential measurement (Savage and Cass, 1984; Andraski and Scanlon, 2002), provided that proper precautions are applied to sensors. This include careful cleaning, handling and calibration of the sensors that are susceptible to acid environment. Special attention should be paid to eliminate the temperature gradients in the sensor during measurements. The current state of the thermocouple psychrometry is presented in (An‐ draski and Scanlon, 2002).The respective sensors are commercially available but the com‐ plexity of measurements and rigid temperature conditions forced on the measurement

There is a number of other moisture measurement methods based on several different phys‐

One of the earliest method of soil moisture measurement, proposed at the end of the 19th century, bases on soil electrical conductivity. However, the electrical conductivity of soil de‐ pends not only on water content, but also on soil salinity, texture, composition and tempera‐ ture (Robinson et al., 2008). On the other hand, when moisture content is known, soil electrical conductivity may be effectively used as a salinity measure. Despite this selectivity issue, soil moisture sensor devices, based on the electrical resistance measurements, are be‐

Electrical resistance blocks are porous bodies comprising of gypsum, nylon or fiberglass, and containing two electrodes, may be used to evaluate soil moisture by measuring electri‐ cal resistance of soil water filling the pores. The soil water fills the pores in order to achieve

ical principles (Hillel, 2004; Robinson et al., 2008; Vereecken et al., 2008).

turns to the ambient (points B and C in Figure 3b).

34 Advances in Agrophysical Research

process make this method not convenient.

**2.5. Other methods of water content measurement**

ing used to evaluate the status of water in the soil.

The appearance of large information banks on soil properties in Europe (Great Britain, France, Holland, Denmark etc.) was provoked by necessity of increasing of agricultural production economics, i.e. the commercial price of soil as the production medium. Protec‐ tion of soil as element of natural environment was the reason of initiating in 1980 year of national program of soil mapping in Norway. The projects of soil monitoring were limit‐ ed to the region of Western Europe and it was evident that later projects should have been integrated in the frame of the whole Europe (Montanarella, 2002). It was realized that soil performs the multitude of functions including supporting plant and animal pro‐ ductivity, maintaining or enhancing water and air quality and supporting human health and habitation, which all define the soil quality (Nortcliff, 2002). Soil quality is usually considered to comprise the following components: physical (texture, dry bulk density, po‐ rosity, aggregate strength and stability, soil compaction and crusting, etc.), chemical (pH, salinity, aeration status, organic matter content, cation exchange capacity, status of plant nutrients, concentration of toxic elements, etc.) and biological (populations of micro-, meso- and macroorganisms, respiration rate or other indicators of microbial activity, etc.). It is evident that almost all mentioned physico-chemical-biological parameters of soil de‐ pend on its moisture. Water is not only the medium, which is necessary for biological changes in evolution of flora and fauna, but it is also the transport medium of heat and energy in the soil (Heitman and Horton, 2011).

depends on the amount of water they contain - water is an inexpensive ingredient, and man‐ ufacturers often try to incorporate as much of it as possible in a food, without exceeding some maximum legal requirement. Also, there are legal limits to the maximum or minimum

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 37

It is therefore important for food scientists to be able to reliably measure moisture contents. A number of analytical techniques have been developed for this purpose, which vary in their accuracy, cost, speed, sensitivity, specificity, ease of operation, etc. The choice of an an‐ alytical procedure for a particular application depends on the nature of the food being ana‐

The need for monitoring physical conditions in agriculture and environment is increasing because of increasing pressure on natural resources, sustainability, exhaustion of nonrenew‐ able resources and climate change. Advances in sensor technology, computers, and commu‐ nication devices results in great amounts of temporal and spatial information that should be processed in real-time (or near real-time) to produce unambiguous information for the deci‐ sion making stage. There are two areas of development in the field of monitoring moisture content of the soil upper layer: ground monitoring stations connected into global networks covering the area of river basins, continents or the whole world (Dorigo et al., 2011) and sat‐ ellite monitoring systems designed especially for the purpose of monitoring water on the Earth, like SMOS (Soil Moisture Ocean Salinity) (Kerr, 2007). Ground monitoring stations tend to use small and wirelessly connected moisture content sensors, while satellite systems process great amount of data on the base of models that must be verified and validated with

Integrated, robust, low-cost, and preferably real-time sensing systems are needed for moni‐ toring physical conditions in agriculture and environment. Commercial products have be‐ come available for some sensor types. Others are currently under development, especially from the view of climate change (Seneviratne et al., 2010) and precision agriculture (Wang et

The technological progress in material science, electronics, telecommunication and informat‐ ics effects in the development of new sensing devices that can be adopted in examining ob‐ jects of agricultural and environmental studies. They include TDR and FDR probes for the simultaneous measurement of soil moisture, electrical conductivity and temperature (Skier‐ ucha et al., 2006). The sensing devices include sensors and transducers, where the former de‐ tects the signal or stimulus and the latter converts input energy of one form into output energy of another form. An example of the sensor is a thermistor giving the change of resist‐ ance as the function of temperature. Such a sensor associated with electrical circuitry forms an instrument, also called a transducer, that converts thermal energy into electrical energy.

*3.3.1. Ground monitoring systems with automated data acquisition and processing*

amount of water that must be present in individual types of food (Tapia et al., 2007).

lysed and the reason the information is needed.

the use of data from ground monitoring stations.

al., 2006).

**3.3. Environmental monitoring**

Agriculture has both positive and negative influence on environment. Its primary func‐ tion is meeting the growing demand for food. Agriculture creates habitats not only for humans but also for wildlife and plays an important role in sequestering carbon, manag‐ ing watersheds and preserving biodiversity. However, agriculture degrades natural re‐ sources by causing soil erosion, introducing unrecoverable hydrological changes, contributing in groundwater depletion, agrochemical pollution, loss of biodiversity, reduc‐ ing carbon sequestration from deforestation and carbon dioxide emissions from forest fires (Doran, 2002).

Physical conditions in agriculture and environment can be defined as physical properties and processes involved in mutual relation between the processes of food and fibre produc‐ tion and the impact of these processes on natural agro-environment. They include topogra‐ phy, surface water and groundwater distributions, heat-temperature distributions, wind direction changes and intensity. There are no universal soil quality indicators developed. It is evident, that they should include water content and/or water potential of the soil as the fundamental parameters. A soil physical parameter defined as the slope of the soil water re‐ tention curve at its inflection point (Dexter, 2004) can be used as an index of soil physical quality that enables different soils and the effects of different management treatments and conditions to be compared directly.

#### **3.2. Quality of food materials and products**

Moisture content (or water activity) affects food quality, i.e. texture, taste, appearance and stability of foods depends on the amount of water they contain. A knowledge of the mois‐ ture content is often necessary to predict the behavior of foods during processing, e.g. mix‐ ing, drying, transportation, flow through a pipe or packaging, storage stability or shelf-life (Bell, 2007; Roudaut, 2007).

The tendency of microorganisms to grow in foods depends on their water content. For this reason many foods are dried below some critical moisture content. The cost of many foods depends on the amount of water they contain - water is an inexpensive ingredient, and man‐ ufacturers often try to incorporate as much of it as possible in a food, without exceeding some maximum legal requirement. Also, there are legal limits to the maximum or minimum amount of water that must be present in individual types of food (Tapia et al., 2007).

It is therefore important for food scientists to be able to reliably measure moisture contents. A number of analytical techniques have been developed for this purpose, which vary in their accuracy, cost, speed, sensitivity, specificity, ease of operation, etc. The choice of an an‐ alytical procedure for a particular application depends on the nature of the food being ana‐ lysed and the reason the information is needed.

#### **3.3. Environmental monitoring**

ed to the region of Western Europe and it was evident that later projects should have been integrated in the frame of the whole Europe (Montanarella, 2002). It was realized that soil performs the multitude of functions including supporting plant and animal pro‐ ductivity, maintaining or enhancing water and air quality and supporting human health and habitation, which all define the soil quality (Nortcliff, 2002). Soil quality is usually considered to comprise the following components: physical (texture, dry bulk density, po‐ rosity, aggregate strength and stability, soil compaction and crusting, etc.), chemical (pH, salinity, aeration status, organic matter content, cation exchange capacity, status of plant nutrients, concentration of toxic elements, etc.) and biological (populations of micro-, meso- and macroorganisms, respiration rate or other indicators of microbial activity, etc.). It is evident that almost all mentioned physico-chemical-biological parameters of soil de‐ pend on its moisture. Water is not only the medium, which is necessary for biological changes in evolution of flora and fauna, but it is also the transport medium of heat and

Agriculture has both positive and negative influence on environment. Its primary func‐ tion is meeting the growing demand for food. Agriculture creates habitats not only for humans but also for wildlife and plays an important role in sequestering carbon, manag‐ ing watersheds and preserving biodiversity. However, agriculture degrades natural re‐ sources by causing soil erosion, introducing unrecoverable hydrological changes, contributing in groundwater depletion, agrochemical pollution, loss of biodiversity, reduc‐ ing carbon sequestration from deforestation and carbon dioxide emissions from forest

Physical conditions in agriculture and environment can be defined as physical properties and processes involved in mutual relation between the processes of food and fibre produc‐ tion and the impact of these processes on natural agro-environment. They include topogra‐ phy, surface water and groundwater distributions, heat-temperature distributions, wind direction changes and intensity. There are no universal soil quality indicators developed. It is evident, that they should include water content and/or water potential of the soil as the fundamental parameters. A soil physical parameter defined as the slope of the soil water re‐ tention curve at its inflection point (Dexter, 2004) can be used as an index of soil physical quality that enables different soils and the effects of different management treatments and

Moisture content (or water activity) affects food quality, i.e. texture, taste, appearance and stability of foods depends on the amount of water they contain. A knowledge of the mois‐ ture content is often necessary to predict the behavior of foods during processing, e.g. mix‐ ing, drying, transportation, flow through a pipe or packaging, storage stability or shelf-life

The tendency of microorganisms to grow in foods depends on their water content. For this reason many foods are dried below some critical moisture content. The cost of many foods

energy in the soil (Heitman and Horton, 2011).

fires (Doran, 2002).

36 Advances in Agrophysical Research

conditions to be compared directly.

(Bell, 2007; Roudaut, 2007).

**3.2. Quality of food materials and products**

The need for monitoring physical conditions in agriculture and environment is increasing because of increasing pressure on natural resources, sustainability, exhaustion of nonrenew‐ able resources and climate change. Advances in sensor technology, computers, and commu‐ nication devices results in great amounts of temporal and spatial information that should be processed in real-time (or near real-time) to produce unambiguous information for the deci‐ sion making stage. There are two areas of development in the field of monitoring moisture content of the soil upper layer: ground monitoring stations connected into global networks covering the area of river basins, continents or the whole world (Dorigo et al., 2011) and sat‐ ellite monitoring systems designed especially for the purpose of monitoring water on the Earth, like SMOS (Soil Moisture Ocean Salinity) (Kerr, 2007). Ground monitoring stations tend to use small and wirelessly connected moisture content sensors, while satellite systems process great amount of data on the base of models that must be verified and validated with the use of data from ground monitoring stations.

Integrated, robust, low-cost, and preferably real-time sensing systems are needed for moni‐ toring physical conditions in agriculture and environment. Commercial products have be‐ come available for some sensor types. Others are currently under development, especially from the view of climate change (Seneviratne et al., 2010) and precision agriculture (Wang et al., 2006).

#### *3.3.1. Ground monitoring systems with automated data acquisition and processing*

The technological progress in material science, electronics, telecommunication and informat‐ ics effects in the development of new sensing devices that can be adopted in examining ob‐ jects of agricultural and environmental studies. They include TDR and FDR probes for the simultaneous measurement of soil moisture, electrical conductivity and temperature (Skier‐ ucha et al., 2006). The sensing devices include sensors and transducers, where the former de‐ tects the signal or stimulus and the latter converts input energy of one form into output energy of another form. An example of the sensor is a thermistor giving the change of resist‐ ance as the function of temperature. Such a sensor associated with electrical circuitry forms an instrument, also called a transducer, that converts thermal energy into electrical energy.

The measurement data collected by the described system are uploaded to and distributed by the International Soil Moisture Network (Dorigo et al., 2011).The ISMN network enables supplementation of the soil moisture data at given locations with other physical parameters

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 39

Remote sensing of water in agricultural and environmental applications means the acquisi‐ tion of relevant information about the condition and state of the land surface by sensors that are not in direct physical contact with it. The data are received mainly in the form of electro‐ magnetic waves reflected from the land surface either in passive mode – when the source of energy is the sun and/or the Earth, or in active mode – when the source energy is artificially generated. The analyzed signal reflected from the land surface is composed of different wavelengths over the electromagnetic spectrum (Huete, 2004). The most important regions

of electromagnetic spectrum for environmental remote sensing are listed in Table 2.

Visible (VIS) 0.4 to 0.7 μm Pigments, chlorophyll, iron Near infrared (NIR) 0.7 to 1.3 μm Canopy structure, biomass Middle infrared (MIR) 1.3 to 3.0 μm Leaf moisture, wood, litter Thermal infrared (TIR) 3 to 14 μm Drought, plant stress Microwave 0.3 to 300 cm Soil moisture, roughness

**Spectral Region Wavelength Application** Ultraviolet (UV) 0.003 to 0.4 μm Air pollutants

**Table 2.** Regions of electromagnetic spectrum used in environmental monitoring (Huete, 2004)

and weeds cover (Thorp and Tian, 2004).

poral frequencies ranging from minutes to weeks or months (Artiola et al., 2004).

Today a large number of satellite sensors observe the Earth at wavelengths ranging from visible to microwave, at spatial resolutions ranging from sub-meters to kilometers and tem‐

The remote sensed data provide information about ecosystem stability, land degradation and desertification (Huete, 2004), carbon cycling (Rosenqvist et al., 2003), soil moisture (Montanarella, 2002; Schmugge et al., 2002; Kerr, 2007), erosion and sediment yield, plant

Water in the soil influences the agricultural productivity as well as the weather and climate. Repeating weather disturbances caused by excessive amount of water or its enduring lack impose the necessity of monitoring water content of soil upper layers and deeper in soil pro‐ files. There is a direct feedback between soil moisture and relative humidity of air. Weather prediction on the base of atmospheric parameters including barometric pressure, tempera‐ ture and air humidity will be more accurate after including soil parameters, like moisture in soil profiles and temperature distribution in the soil. Although water in the soil has a minor contribution of the water balance in the continents, it greatly influences the global water bal‐

(so called metadata).

*3.3.2. Remote sensing*

**Figure 4.** Temporal variability of soil moisture and temperature in P4 localization in Polesie National Park during the period 03.2008 – 02.2010

Another important element of a ground monitoring system is a data acquisition and proc‐ essing unit, which monitors the output signal of the transducer and processes the resulting data into a form that can be understood by the end user. The basic features of this unit in‐ clude user friendly interfaces for the operator, large storage memory, physical communica‐ tion interfaces preferably with serial transmission from the instrument to the operator's notebook. Telemetry with the application of wireless networks is becoming popular espe‐ cially for distant ground monitoring systems (Wang et al., 2006).

Monitoring stations must meet strong requirements concerning power consumption. The hardware designers should use low power electronic circuits and apply sleep mode opera‐ tions whenever possible. Also, charging the internal battery may be accomplished with a so‐ lar panel.

Figure 4 presents a sample graph of time variability of the values of moisture and tempera‐ ture of the soil in the P4 measurement point (rendzina soil) in the Polesie National Park in eastern Poland collected by monitoring stations of soil moisture, temperature and electrical conductivity (not presented in Figure 4).

The measurement data collected by the described system are uploaded to and distributed by the International Soil Moisture Network (Dorigo et al., 2011).The ISMN network enables supplementation of the soil moisture data at given locations with other physical parameters (so called metadata).

#### *3.3.2. Remote sensing*

**Figure 4.** Temporal variability of soil moisture and temperature in P4 localization in Polesie National Park during the

Another important element of a ground monitoring system is a data acquisition and proc‐ essing unit, which monitors the output signal of the transducer and processes the resulting data into a form that can be understood by the end user. The basic features of this unit in‐ clude user friendly interfaces for the operator, large storage memory, physical communica‐ tion interfaces preferably with serial transmission from the instrument to the operator's notebook. Telemetry with the application of wireless networks is becoming popular espe‐

Monitoring stations must meet strong requirements concerning power consumption. The hardware designers should use low power electronic circuits and apply sleep mode opera‐ tions whenever possible. Also, charging the internal battery may be accomplished with a so‐

Figure 4 presents a sample graph of time variability of the values of moisture and tempera‐ ture of the soil in the P4 measurement point (rendzina soil) in the Polesie National Park in eastern Poland collected by monitoring stations of soil moisture, temperature and electrical

cially for distant ground monitoring systems (Wang et al., 2006).

conductivity (not presented in Figure 4).

period 03.2008 – 02.2010

38 Advances in Agrophysical Research

lar panel.

Remote sensing of water in agricultural and environmental applications means the acquisi‐ tion of relevant information about the condition and state of the land surface by sensors that are not in direct physical contact with it. The data are received mainly in the form of electro‐ magnetic waves reflected from the land surface either in passive mode – when the source of energy is the sun and/or the Earth, or in active mode – when the source energy is artificially generated. The analyzed signal reflected from the land surface is composed of different wavelengths over the electromagnetic spectrum (Huete, 2004). The most important regions of electromagnetic spectrum for environmental remote sensing are listed in Table 2.


**Table 2.** Regions of electromagnetic spectrum used in environmental monitoring (Huete, 2004)

Today a large number of satellite sensors observe the Earth at wavelengths ranging from visible to microwave, at spatial resolutions ranging from sub-meters to kilometers and tem‐ poral frequencies ranging from minutes to weeks or months (Artiola et al., 2004).

The remote sensed data provide information about ecosystem stability, land degradation and desertification (Huete, 2004), carbon cycling (Rosenqvist et al., 2003), soil moisture (Montanarella, 2002; Schmugge et al., 2002; Kerr, 2007), erosion and sediment yield, plant and weeds cover (Thorp and Tian, 2004).

Water in the soil influences the agricultural productivity as well as the weather and climate. Repeating weather disturbances caused by excessive amount of water or its enduring lack impose the necessity of monitoring water content of soil upper layers and deeper in soil pro‐ files. There is a direct feedback between soil moisture and relative humidity of air. Weather prediction on the base of atmospheric parameters including barometric pressure, tempera‐ ture and air humidity will be more accurate after including soil parameters, like moisture in soil profiles and temperature distribution in the soil. Although water in the soil has a minor contribution of the water balance in the continents, it greatly influences the global water bal‐ ance (Seneviratne et al., 2010). Therefore, to increase weather prediction and protect people from weather cataclysms, it is necessary to collect and process data about soil moisture from ground and satellite measurements (Dorigo et al., 2011).

[3] Lewicki PP. Water as the determinant of food engineering properties. A review. Jour‐

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[4] Chen Y, Or D. Effects of Maxwell-Wagner polarization on soil complex dielectric per‐ mittivity under variable temperature and electrical conductivity. Water Resources

[5] Tapia MS, Alzamora SM, Chirife J. Effects of water activity (aw) on microbial stabili‐ ty: as a hurdle in food preservation. In: Barbosa-Cánovas GV, Fontana AJJ, Schmidt SJ, Labuza TP. (eds.) Water activity in foods. Fundamentals and applications. Ames, USA: Blackwell Publishing and the Institute of Food Technologists; 2007. p239–271.

[6] Or D, Wraith JM. Soil Water Content and Water Potential Relationships. In: Warrick AW. (ed.) Soil physics companion. Boca Raton, Florida, USA: CRC Press LLC; 2002.

[7] Malicki MA. Methodical questions of monitoring of water status in selected biologi‐

[8] Blahovec J. Water in forming agricultural products. In: Glinski J, Horabik J, Lipiec J. (eds.) Encyclopedia of Agrophysics. Dordrecht, The Netherlands: Springer; 2011.

[9] Skierucha W. Temperature dependence of time domain reflectometry-measured soil dielectric permittivity. Journal of Plant Nutrition and Soil Science 2009;172(2) 186–

[10] Skierucha W, Wilczek A. A FDR sensor for measuring complex soil dielectric permit‐ tivity in the 10–500 MHz frequency range. Sensors (Basel, Switzerland) 2010;10(4)

[11] Vereecken H, Huisman JA, Bogena H, Vanderborght J, Vrugt JA, Hopmans JW. On the value of soil moisture measurements in vadose zone hydrology: A review. Water

[12] Jackson TJ, Schmugge J, Engman ET. Remote sensing applications to hydrology: soil

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scopy (NIRS). European Journal of Soil Science 2009;60(5) 770–784.

cal materials (in Polish). Lublin: Institute of Agrophysics PAS; 1999.

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193.

Monitoring of soil temperature, which is one of the most important physical parameter apart from water content or water matrix potential, is not a technical problem. There are var‐ ious temperature sensors available including electronic ones that enable automatic measure‐ ment.

## **4. Summary**

Aquametry in agrophysics integrates a number of interdisciplinary research and application issues, including: the state of water in soil and biomaterials, construction of the sensors and physical principles of applied measurement techniques, accuracy and representativeness. There is no universal recipe to determine the amount of water in a sample of material, be‐ cause the objects of interest in agrophysics differ in scale, observation time, texture, temper‐ ature, required accuracy, etc. Therefore, there are so many measurement principles and techniques, each optimized to the object of interest, required measurement conditions, tem‐ poral and dimensional scales, and the function of the final information.

The current aquametry tools reflect actual state of technology development and they will continuously change. The information about water in the term of its quantity and quality is crucial for sustainable development, environmental protection and food production since water is not only the basic ingredient of food, but also is a vital element of our habitat. The received and processed data increase our knowledge for the benefit of social, political and economic sustainable development, security as well as for better understanding the nature.

## **Author details**

Wojciech Skierucha\* , Agnieszka Szypłowska and Andrzej Wilczek

\*Address all correspondence to: w.skierucha@ipan.lublin.pl

Institute of Agrophysics, Polish Academy of Sciences, Lublin, Poland

## **References**


[3] Lewicki PP. Water as the determinant of food engineering properties. A review. Jour‐ nal of Food Engineering 2004;61(4) 483–495.

ance (Seneviratne et al., 2010). Therefore, to increase weather prediction and protect people from weather cataclysms, it is necessary to collect and process data about soil moisture from

Monitoring of soil temperature, which is one of the most important physical parameter apart from water content or water matrix potential, is not a technical problem. There are var‐ ious temperature sensors available including electronic ones that enable automatic measure‐

Aquametry in agrophysics integrates a number of interdisciplinary research and application issues, including: the state of water in soil and biomaterials, construction of the sensors and physical principles of applied measurement techniques, accuracy and representativeness. There is no universal recipe to determine the amount of water in a sample of material, be‐ cause the objects of interest in agrophysics differ in scale, observation time, texture, temper‐ ature, required accuracy, etc. Therefore, there are so many measurement principles and techniques, each optimized to the object of interest, required measurement conditions, tem‐

The current aquametry tools reflect actual state of technology development and they will continuously change. The information about water in the term of its quantity and quality is crucial for sustainable development, environmental protection and food production since water is not only the basic ingredient of food, but also is a vital element of our habitat. The received and processed data increase our knowledge for the benefit of social, political and economic sustainable development, security as well as for better understanding the nature.

, Agnieszka Szypłowska and Andrzej Wilczek

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\*Address all correspondence to: w.skierucha@ipan.lublin.pl

Institute of Agrophysics, Polish Academy of Sciences, Lublin, Poland

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**4. Summary**

40 Advances in Agrophysical Research

**Author details**

Wojciech Skierucha\*

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**Chapter 3**

**Time Stability of Soil Water Content**

Wei Hu, Lindsay K. Tallon, Asim Biswas and

Additional information is available at the end of the chapter

Soil water is a key variable controlling water and energy fluxes in soils (Vereecken et al., 2007). It is necessary for plant and vegetation growth and development. Research has indi‐ cated that soil water content (*SWC*) varies both in space and time. Variations in both space and time present a substantial challenge for applications such as precision agriculture and

Since the contribution of Vachaud et al. (Vachaud et al., 1985), a large body of research has indicated the presence of time stability of *SWC* (Biswas and Si, 2011c; Comegna and Basile, 1994; Grayson and Western, 1998; Hu et al., 2009; Martínez-Fernández and Ceballos; 2005; Mohanty and Skaggs, 2001), which means that the spatial pattern of *SWC* does not change with time at a certain probability. According to this concept, if a field is repeatedly surveyed for *SWC*, there is a high probability that a location with certain wetness characteristics (i. e., wet, dry, intermediate) will maintain those characteristics on subsequent occasions. Time stability has also been extended to describe the characteristics of *SWC* at point scales. A loca‐ tion will be regarded as time stable provided it can estimate the average *SWC* of an area.

Time stability of *SWC* has been observed at a large variety of scales ranging from plot (Pa‐ chepsky et al., 2005) to region (Martínez-Fernández and Ceballos, 2003) and related studies cover a range of investigated areas, sampling schemes, sampling depths, investigation peri‐ ods, and land uses (Biswas and Si; 2011c; Brocca et al., 2009; Cosh et al., 2008; Hu et al., 2010a;Tallon and Si, 2004; Vachaud et al., 1985). As a result, a variety of methods have been developed to evaluate time stability of *SWC*, each with its own advantages and disadvantag‐ es. Time stability is usually used to characterize time persistence of the spatial pattern of *SWC* between measurement occasions, either at the measurement scale or at different scales (Biswas and Si, 2011c; Cosh et al., 2006; Kachanoski and De Jong, 1988; Vachaud et al., 1985).

> © 2013 Hu et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

© 2013 Hu et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

distribution, and reproduction in any medium, provided the original work is properly cited.

Bing Cheng Si

**1. Introduction**

soil water management.

http://dx.doi.org/10.5772/52469

**Chapter 3**
