**5. Soil moisture sources**

*Soil Moisture Importance*

**88**

**Figure 5.**

**Figure 4.**

*sinkholes supplied by runoff water (right).*

*Soil desiccation and cracking (left), aromatic plant root adaptation to arid land (middle), and very fertile* 

*Economically important crop Vitis vinifera L. on plantation under drip irrigation (left: Cover crop system with irrigation) and individual farm with open filed crop growing system (right: Consequences of drought).*

weak growth and progression but manage to survive dry periods. Because water in deserts does not stay in one place for long and often drains very quickly, without roots penetrating deep into the soil succulents depend on the root network close to the surface (the first 5–40 cm below the surface) to collect most of the water after rain. Therefore, many species of cactus, agaves, and other succulents' groups have many shallow and extremely widespread roots, which is an adaptation to rains that are sudden and short-lived. Within a few hours after the rain comes, many additional fast-growing lateral roots appear that have thin walls and increase water absorption. When water disappears, they degrade [41, 42]. Often, as an example of a droughtadapted plant, one specific plant, the Jericho rose or *Anastatica hierochuntica*, is found in the list. In addition, succulents were defined by their morphological characteristics, it is important to define them from an eco-physiological point of view: succulents plants have ability to survive in a water-restricted habitat using special strategies for water use. Succulents can be in different life forms (annuals or perenni-

als, shrubs, and trees) and from completely different genera and families.

Some economically important plants do not have the ability to adapt to drought (**Figure 4**), such as the aforementioned wild plants of arid areas. In complete lack of water or prolonged drought, they dry out completely and die. In addition, during periods of water deficits, these plants show a completely different course of development, in a way that they often discard their leaves and fruits and slow down growth. Therefore, it is extremely important that plants receive adequate amounts of moisture during growth and development in order to be able to optimize the level of expected yield. Moisture from the soil is a much more favorable factor that affects the uptake and utilization of water in the plant compared to the moisture that the plant receives through precipitation [42, 43]. The biological importance of precipitation for the plant itself is questioned, because short-term rainfall does not have high efficiency, unlike longer weather conditions or sudden precipitation,

Soil supplied with moisture from the atmosphere and/or from deeper soil layers. The precipitation from atmosphere could be in the form of rainfall, snow, ice rain of some other forms in which riches the soil. From the deeper layers of the soil, the earth was supplied from groundwater. Groundwater was created by the underground discharge of water from precipitation from the hills to the lowlands. Sometimes these waters can appear on the surface, which we call natural springs. Groundwater varies in its depth. The one located 1–2 m below the soil surface is very useful for plants because it protects them from drought. The agroclimatology as a science pays more and more attention to temporal and spatial variations of moisture as an essential element in the surface distribution of moisture and energy source that are reflected in the complete ecosystem influencing the soil-plantatmosphere continuum [44].

All soils are water permeable, because water can move through the space of interconnected pores between solid particles. Soil moisture behavior due to gravity and other factors such as moisture quantity, distribution, and moisture pressure significantly affect soil properties. In conditions when the soil was saturated with moisture, all soil pores are filled with water, and gases are expelled, which often results in anoxia in plants, especially if the water overloading conditions are prolonged. If not, all pores ware filled with water; the soil is partially saturated or unsaturated. The highest plant yields are achieved when the most favorable ratio of air and water in the soil was achieved and especially in the critical periods of each crop [45]. Since different plant species may have different water needs, which also depend on the developmental stages of each plant, it is necessary to provide the required amount of water in critical periods of plant [44]. Climatic characteristics and soil water regime and their interrelationship is hard to have in balance due to the high production needs, as the most of the agriculture land is placed in arid area [46]. Regarding the arable agriculture land, the total of 1.5 billion hectares were estimated, which about 250 million are under irrigation or about 17% total used land and for agricultural food production is estimated about 40% [47]. It was estimated that between 2000 and 2500 km3 of water is consumed annually for irrigation. It is a well-known fact that on a global scale, about 70% of the affected quantities of water were consumed for agriculture [3], and irrigation is the main consumer of that water.

Water uptake relays on the osmotic potential of the soil solution, and the decrease in uptake can occur in the summer months on saline soils. At low temperatures, water uptake was reduced and then the plants experience physiological drought. This phenomenon can often occur in the spring; when due to the relatively high air temperature and low soil temperature, there is an imbalance in the water regime of plants, despite the fact that the soil contains sufficient amounts of water.

#### **5.1 Soil water type**

Water that results from precipitation or flooding was called surface water and it causes erosion and landslides. Free and bound water were most occurred states of soil water. The bounded water can occurred as: chemically bound water, hygroscopic water, membrane water, water in the form of water vapor and capillary water, while the free water includes gravitational, groundwater, and water in the form of ice [48]. Water in the soil is bound by various forces that the root system must overcome when adopted, so the water in the soil is divided into two classes: accessible and inaccessible.

Bound water in the soil is in the following forms:


**91**

*Water Plant and Soil Relation under Stress Situations DOI: http://dx.doi.org/10.5772/intechopen.93528*

action between the soil particles and the absorbed water.

period. She then swells with the help of her own weight.

great impact on plants and soil if it contains soluble salts.

have a negative effect on the soil.

**5.2 Movement of water in the soil**

2.Groundwater that is under a certain pressure in a water-permeable layer between water-impermeable layers. Groundwater is another form of free water and it formed if gravitational water encounters an impermeable layer of soil. Groundwater can also be associated with river water and then this water is close to the surface (1.0–2.5 m). The impact of groundwater on the soil depends on its depth and composition. Groundwater has no significance for plants if it is at great depth, but if it is located high and too close to the soil surfaces, it has a negative effect on plants. Groundwater is useful to plants when it is accessible to the roots due to capillary uplift or when the plants can absorb water from the deeper layer with long root system. Groundwater has a

3.Ice form water or water in solid form is a special form of free water. This form of water is not of great importance for our climatic areas. Freezing and melting

The three basic forms of water movement in liquid form are capillary movement, infiltration, and filtration. The movement of water is possible through unsaturated and saturated soil. Movement is possible descending, ascending, and lateral. The water direction of movement and speed were highly related to the occurrence state of the water, amount, texture, structure, porosity, the amount of organic matter, and the forces that cause the movement. The primary causes of soil

The capillary movement of water occurs from the area of higher humidity to the

water movement are capillary forces, gravity, and hydrostatic pressure.

area of lower humidity, that is, in unsaturated soil in micropores.

Free water in the soil is in the following forms: gravitational, groundwater, and ice-shaped water. For all forms of free water, one thing is common and that is when they are in liquid form, they move laterally and vertically under the influence of inclination or under the influence of gravity. The forces that hold water against soil particles are on the one hand the tension of moisture (surface, hydrostatic, and gravitational forces), and on the other hand, the osmotic pressure of the aqueous phase of the soil. Cohesion forces connect water molecules (hydrogen bridges and Van der Waals-London forces), whereas adhesion is responsible for their binding to soil particles and the formation of a double layer. Adhesion water is water that is located in the surface soil layer and retained by the forces of mutual molecular

1.Gravitational or leach water is formed in occasion of fully saturated soil pores with water. In such a state of saturation, water seeps through macropores by gravity and is not bound to the soil. Gravitational water is the basic form of free water in the soil. After the precipitation lager, soil pores were fulfilled and, under the gravity, flows into the depth or sideways, down the slope. The size of the pores in the soil or soil texture was highly dependent on water flow movement in soil profile. If the soil has a lighter mechanical composition and contains a higher content of noncapillary pores, gravitational water will pass through the soil faster and less water will remain in the soil. There are two forms of gravitational water: fast gravitational water (for larger pores) and water that gradually drains away (for smaller pores). Gravitational water can be retained in the smallest noncapillary pores for several days during the wet

*Water Plant and Soil Relation under Stress Situations DOI: http://dx.doi.org/10.5772/intechopen.93528*

*Soil Moisture Importance*

accessible and inaccessible.

available to the plant.

Bound water in the soil is in the following forms:

crystallized water. If water in the form of H+

surface forces at a relative humidity of 95–100%.

states of soil water. The bounded water can occurred as: chemically bound water, hygroscopic water, membrane water, water in the form of water vapor and capillary water, while the free water includes gravitational, groundwater, and water in the form of ice [48]. Water in the soil is bound by various forces that the root system must overcome when adopted, so the water in the soil is divided into two classes:

1.Chemically bound water has no significance for the plant because it was bound within a solid lattice of minerals and as such belongs to the solid phase of the soil. Chemically bound water does not participate in physical processes and does not evaporate at a temperature of 100° C. It is present as constitutive and

tion of different minerals, it was called crystal water. If it is bound to minerals as a molecule, then it is constitutional water. Chemically bound water is not

2.Hygroscopic water is water that is adsorbed on absolutely dry soil by surface forces at a relative humidity of less than 100%. The ability of soil particles to absorb relative moisture from the air was called hygroscopic water. Hygroscopic water in the soil is held at a high pressure of 50 bar; since the suction force of the root system is between 6 and 16 bar, it is inaccessible to plants. Maximum hygroscopic water is water constant but has no practical application other than being used to calculate other water constants. It is also adsorbed on dry soil by

3.Membrane or film water is located around soil particles and is used by plants only when the soil dries to membrane moisture. Membrane water binds to the surface of the particle after completion, that is, saturation of water binding to the maximum hygroscopy, if the particles can attract and to what extent there is available water. It was water bound by dipole forces that were weakening toward the periphery. Limestone water moves very slowly in the soil. According to Škorić [49], it is possible to divide film water into: stationary film water that corresponds to twice the value of hygroscopy and is inaccessible to plants, and mobile film water, where the water membrane is thick enough for water to move through plants is affordable. There are different zones: hygroscopic, which do forces greater than 50 bar, lentocapillary (6.25–50 bar) and mem-

brane water of 0.50–6.25 bar hold, which is accessible to the plant.

4.Water in a gaseous state (water vapor) is physiologically useful if it turns into a liquid state by condensation, and it is a constant component of the soil air. The air in the soil saturated with water vapor with 98%. Water vapor in the soil moves from a warmer to a colder area or from an area of higher tension to

5.Capillary water is very mobile and is of great importance in providing plants with water, as well as for physical and chemical processes in the soil. In dry climates, it is the only reserve for the plant, and the measures that allow the retention of capillary water were deep tillage, application of mulch, and cultivation. Capillary water is water that fills the narrowest pores of the soil due to the action of surface tension and occurs by increasing soil moisture. Capillary water is the most ecologically important form of water and is a basic factor in

and OH−

ions enters the composi-

**90**

lower tension.

soil dynamics and fertility.

Free water in the soil is in the following forms: gravitational, groundwater, and ice-shaped water. For all forms of free water, one thing is common and that is when they are in liquid form, they move laterally and vertically under the influence of inclination or under the influence of gravity. The forces that hold water against soil particles are on the one hand the tension of moisture (surface, hydrostatic, and gravitational forces), and on the other hand, the osmotic pressure of the aqueous phase of the soil. Cohesion forces connect water molecules (hydrogen bridges and Van der Waals-London forces), whereas adhesion is responsible for their binding to soil particles and the formation of a double layer. Adhesion water is water that is located in the surface soil layer and retained by the forces of mutual molecular action between the soil particles and the absorbed water.


#### **5.2 Movement of water in the soil**

The three basic forms of water movement in liquid form are capillary movement, infiltration, and filtration. The movement of water is possible through unsaturated and saturated soil. Movement is possible descending, ascending, and lateral. The water direction of movement and speed were highly related to the occurrence state of the water, amount, texture, structure, porosity, the amount of organic matter, and the forces that cause the movement. The primary causes of soil water movement are capillary forces, gravity, and hydrostatic pressure.

The capillary movement of water occurs from the area of higher humidity to the area of lower humidity, that is, in unsaturated soil in micropores.

Infiltration is the uneven absorption by vertical and lateral motion into unsaturated soil, by the action of capillary, gravitational, and osmotic forces.

Filtration is the leaching of excess water from saturated soil into deeper layers through soil macropores, which causes gravity (and hydrostatic pressure).

Water in the soil moves in three basic directions: descending, ascending, and lateral. The descending flow of water is downward, with water draining freely through the macropores of the soil, primarily under the influence of gravitational force. This steady flow of water in cultural engineering corresponds to the concept of filtration. The ascending movement of water is ascending toward the soil surface and interpreted by capillary theory, membrane water theory, or potential difference (suction force—tension). According to capillary theory, water rises in profile due to the adhesion force that occurs between soil and water particles. Due to the adhesion, the capillaries fill and the water rises with the strength of the meniscus (adhesion) and due to the surface tension. According to the theory of membrane water, the ions in the outer diffuse shell have a suction power (osmosis) that fills the capillaries. Soil particles that have a thinner mantle accept water than those with a larger mantle. The last is the potential theory where water moves due to tension from a wetter to drier area. Lateral (lateral and radial) movement of water is interpreted by capillary theory, the theory of membrane water, and osmotic pressure, and the theory of potential.

The supply of soil with water from deeper soil layers depends on the type and composition but also on the method of soil cultivation depending on its purpose. Precipitation, which falls to the ground, is not equally abundant everywhere. Long-term hydrometeorological and agrometeorological measurements determine the daily, monthly, and annual average amount of precipitation for a particular area, which is logical to vary from place to place. Almost half of the water that enters the soil evaporates out into the atmosphere, about 2/6 is lost by leaching and runoff into depressions, streams, streams, and various standing waters, while only 1/6 is absorbed into the soil, which means that about 1/6 of the total precipitation and moisture that enters the soil remains available to the plants. Water retention is a very important factor in soil composition. This means that, for example, sandy soils differ significantly from clay soils in terms of moisture retention, absorption, and loss. Every soil has a certain degree of porosity because the soil made up of tiny fractions of sand and even tiny dust particles. Depending on the sand fraction, the pore size will also vary, or the permeability rate of such soil. Clay soil, on the other hand, consists largely of the finest particles of powder and clay, between which a very small number and diameter of pores were formed or have the ability to form, which limits the porosity of this type of soil.

#### **5.3 Soil water constants**

Water or hydrological constants defined as the equilibrium states between the suction force of soil particles and water. Most authors include the following in water constants:

**93**

McLane [52].

*Water Plant and Soil Relation under Stress Situations DOI: http://dx.doi.org/10.5772/intechopen.93528*

• Lento-capillary point (humidity) or wilting point.

tion and primarily for irrigation and drainage were listed here.

Water retention and water movement in soil were characterized by above mentioned water constants. Water constants were defined as the concept of water content, shape, and form in the soil related to the texture and structure of the soil, organic matter content, and applied agrotechnical measures. There were a number of water constants and various names were used in the literature and practice. Water constants that are of practical importance for the needs of soil hydro meliora-

Hygroscopic water is, as mentioned earlier, the ability of soil particles to absorb relative moisture from the air. Humidity in contact with dry soil, allows the absorption of moisture that increases the volume of soil particles, until an equilibrium ratio is achieved. The established ratio represents the maximum absorption capacity with the achieved maximum hygroscopic effect, which for soils with sandy texture is 1%, for loamy soil texture up to 7%, and for clay soil texture up to 17% measured on dry matter. There is a difference between the maximum hygroscopy (Hm) according to Lebedev [50] and the hygroscopy according to Mitscherlich [51] (Hy). If the soil is placed in the conditions of complete saturation of the air with water vapor, then it will attract the maximum layer of hygroscopic water, this called maximum hygroscopy. Mitscherlich hygroscopy [51] corresponds to the moisture content, which is obtained by placing a soil sample in an evacuated desiccator above 10% sulfuric acid. The acid creates conditions of 96% relative humidity of the air that the soil absorbs. After establishing the equilibrium state by gravimetric method by weighing the moistened sample to hygroscopic moisture and completely dry soil, and by calculation in mass percentages, the moisture content corresponding to the hygroscopy is obtained. Hygroscopic moisture held in the soil, as mentioned earlier, by a suction force of 50 bar and is inaccessible to plants because the root of the plant has a suction force between 6 and 16 bar. The double value of Mitscherlich hygroscopy corresponds to the equilibrium state between

the suction force of the plant root and the soil particles called the wilting point. Soil water capacity presents a soil capacity for water retention in micropores after squeezing water from macropores under the influence of gravity. Depending on the method of determination, there were retention and absolute, field soil water capacity, minimum water capacity, and moisture equivalent according to Briggs and

Maximum soil water capacity (MWC) is a constant that represents the water content in the soil when water saturation is in maximum fulfilling the micropores and they are theoretically equal to the total porosity (**Figure 3**). When the maximum water capacity is then all other water constants were maximally realized. The state of maximum water capacity is short, especially in normal soils. Maximum water capacity is undesirable because anaerobic conditions occur, which puts the plants in a state of stress and puts maximum pressure on the metabolic activities of the plant. MWC occurs due to heavy rains and sudden melting of snow. In addition, the soil maximally saturated with water both when groundwater reaches the surface and during major floods. In rare situations and for a short period, the soil saturated to the MWC value. When the soil oversaturated with water, oxygen is lost in the soil and anaerobic conditions occur. This phenomenon is very harmful to soil and plants.

• Field water capacity for soil

• Humidity equivalent

• Minimum water capacity for soil


*Water Plant and Soil Relation under Stress Situations DOI: http://dx.doi.org/10.5772/intechopen.93528*


*Soil Moisture Importance*

and the theory of potential.

which limits the porosity of this type of soil.

**5.3 Soil water constants**

• Hygroscopic water form

• Maximum water capacity for soil

• Water retention and absolute water capacity for soil

• Soil water capacities

constants:

Infiltration is the uneven absorption by vertical and lateral motion into unsatu-

Filtration is the leaching of excess water from saturated soil into deeper layers

Water in the soil moves in three basic directions: descending, ascending, and lateral. The descending flow of water is downward, with water draining freely through the macropores of the soil, primarily under the influence of gravitational force. This steady flow of water in cultural engineering corresponds to the concept of filtration. The ascending movement of water is ascending toward the soil surface and interpreted by capillary theory, membrane water theory, or potential difference (suction force—tension). According to capillary theory, water rises in profile due to the adhesion force that occurs between soil and water particles. Due to the adhesion, the capillaries fill and the water rises with the strength of the meniscus (adhesion) and due to the surface tension. According to the theory of membrane water, the ions in the outer diffuse shell have a suction power (osmosis) that fills the capillaries. Soil particles that have a thinner mantle accept water than those with a larger mantle. The last is the potential theory where water moves due to tension from a wetter to drier area. Lateral (lateral and radial) movement of water is interpreted by capillary theory, the theory of membrane water, and osmotic pressure,

The supply of soil with water from deeper soil layers depends on the type and composition but also on the method of soil cultivation depending on its purpose. Precipitation, which falls to the ground, is not equally abundant everywhere. Long-term hydrometeorological and agrometeorological measurements determine the daily, monthly, and annual average amount of precipitation for a particular area, which is logical to vary from place to place. Almost half of the water that enters the soil evaporates out into the atmosphere, about 2/6 is lost by leaching and runoff into depressions, streams, streams, and various standing waters, while only 1/6 is absorbed into the soil, which means that about 1/6 of the total precipitation and moisture that enters the soil remains available to the plants. Water retention is a very important factor in soil composition. This means that, for example, sandy soils differ significantly from clay soils in terms of moisture retention, absorption, and loss. Every soil has a certain degree of porosity because the soil made up of tiny fractions of sand and even tiny dust particles. Depending on the sand fraction, the pore size will also vary, or the permeability rate of such soil. Clay soil, on the other hand, consists largely of the finest particles of powder and clay, between which a very small number and diameter of pores were formed or have the ability to form,

Water or hydrological constants defined as the equilibrium states between the suction force of soil particles and water. Most authors include the following in water

rated soil, by the action of capillary, gravitational, and osmotic forces.

through soil macropores, which causes gravity (and hydrostatic pressure).

**92**

• Lento-capillary point (humidity) or wilting point.

Water retention and water movement in soil were characterized by above mentioned water constants. Water constants were defined as the concept of water content, shape, and form in the soil related to the texture and structure of the soil, organic matter content, and applied agrotechnical measures. There were a number of water constants and various names were used in the literature and practice. Water constants that are of practical importance for the needs of soil hydro melioration and primarily for irrigation and drainage were listed here.

Hygroscopic water is, as mentioned earlier, the ability of soil particles to absorb relative moisture from the air. Humidity in contact with dry soil, allows the absorption of moisture that increases the volume of soil particles, until an equilibrium ratio is achieved. The established ratio represents the maximum absorption capacity with the achieved maximum hygroscopic effect, which for soils with sandy texture is 1%, for loamy soil texture up to 7%, and for clay soil texture up to 17% measured on dry matter. There is a difference between the maximum hygroscopy (Hm) according to Lebedev [50] and the hygroscopy according to Mitscherlich [51] (Hy). If the soil is placed in the conditions of complete saturation of the air with water vapor, then it will attract the maximum layer of hygroscopic water, this called maximum hygroscopy. Mitscherlich hygroscopy [51] corresponds to the moisture content, which is obtained by placing a soil sample in an evacuated desiccator above 10% sulfuric acid. The acid creates conditions of 96% relative humidity of the air that the soil absorbs. After establishing the equilibrium state by gravimetric method by weighing the moistened sample to hygroscopic moisture and completely dry soil, and by calculation in mass percentages, the moisture content corresponding to the hygroscopy is obtained. Hygroscopic moisture held in the soil, as mentioned earlier, by a suction force of 50 bar and is inaccessible to plants because the root of the plant has a suction force between 6 and 16 bar. The double value of Mitscherlich hygroscopy corresponds to the equilibrium state between the suction force of the plant root and the soil particles called the wilting point.

Soil water capacity presents a soil capacity for water retention in micropores after squeezing water from macropores under the influence of gravity. Depending on the method of determination, there were retention and absolute, field soil water capacity, minimum water capacity, and moisture equivalent according to Briggs and McLane [52].

Maximum soil water capacity (MWC) is a constant that represents the water content in the soil when water saturation is in maximum fulfilling the micropores and they are theoretically equal to the total porosity (**Figure 3**). When the maximum water capacity is then all other water constants were maximally realized. The state of maximum water capacity is short, especially in normal soils. Maximum water capacity is undesirable because anaerobic conditions occur, which puts the plants in a state of stress and puts maximum pressure on the metabolic activities of the plant. MWC occurs due to heavy rains and sudden melting of snow. In addition, the soil maximally saturated with water both when groundwater reaches the surface and during major floods. In rare situations and for a short period, the soil saturated to the MWC value. When the soil oversaturated with water, oxygen is lost in the soil and anaerobic conditions occur. This phenomenon is very harmful to soil and plants.

Excess water in the soil causes problems in the plant's oxygen supply (occurrence of anoxia = complete lack of oxygen and occurrence of hypoxia = reduced amounts of oxygen). Anoxia occurs more often if the temperature 12°C of the air is above 20°C, when the consumption of oxygen by breathing the roots of plants, soil fauna, and microorganisms is higher than at lower temperatures. Under such anaerobic conditions or at insufficient oxygen concentration, changes in the metabolism of plant tissue cells occur. Cell intoxication with alcoholic fermentation products and increase in cytoplasm acidity occurs. These phenomena can result in cell death. Plants suffering from the lack of oxygen show signs of wilting, due to the inability to active transfer water, and the leaves show epinastic growth (downward) due to increased ethylene synthesis. In such leaves, the concentration of abscisic acid increased, which initiates the closure of the shoot. This interrupts the transpiration flow and distribution of osmolytes and water to up ground plant parts which resulting in growth retardation.

The absolute soil water capacity according to Kopecky [53] corresponds to the water content in the micropores after complete saturation of the sample in a cylinder with a volume of 100 cm3 and squeezing of excess water from the soil macropores after 24 hours. Horvat et al. [54] introduced the retention capacity of soil for water due to certain soil losses in determining the absolute capacity. According to this method, the soil sample in the cylinder, according to Kopecky [53] placed on a stand with filter papers whose edges immersed in water. The soil absorbs water and holds it in the micropores by adhesion, hydration, capillary, and surface tension forces. After squeezing, the excess water from the gravitational pores (the soil sample stands on the filter paper for half an hour) and the water content in volume % which corresponds to the retention capacity of the soil for water are is determined gravimetrically. The values of absolute and retention capacity of soil for water correspond to the soil layer above the groundwater level and are higher than those determined in field condition.

Field water capacity (FWC) is a condition where micropores are filled with water and macropores with air, after maximum saturation and seepage of free water under the influence of gravity. Soil moisture at FWC is retaining longer provided there is no evaporation or the influence of groundwater (capillary). For field water capacity, there are many names such as retention capacity, maximum water capacity, capillary capacity, and water retention at 0.33 bar. However, this constant (FWC) is determined in field conditions, and therefore, the name filed water capacity is the most appropriate (**Figure 6**). Field water capacity is extremely important because

**95**

**Figure 7.**

*Water Plant and Soil Relation under Stress Situations DOI: http://dx.doi.org/10.5772/intechopen.93528*

correspond to the actual water content of the soil.

*Philodendron in well turgid (left) and in less turgid condition (right).*

its knowledge used in various calculations in the design and use of hydromelioration systems. FWC is especially important for irrigation because it is water constant without is impossible to accurate calculate the irrigation rate to moisten the active rhizosphere. FWC is also the largest amount of water that can be giving during irrigation because water above the FWC value is considered harmful to the plant. Irrigation practice depends on soil conditions, moisture and plant's requirements. Field capacity corresponds to the state of moisture that occurs in the soil immediately after rain, before evaporation and transpiration begin. It is expressed as the percentage of water in the soil that is found in such a state of humidity. Therefore, it corresponds to the water content in the well-drained, permeable soil from which all the gravitational water had drained. However, soil moisture that would correspond to the absence of gravitational water alone must be determined relatively soon after rain. This is possible only with light and well-drained soils, because in others, the process of rain infiltration through the ecological profile takes a long time, often several days. Meanwhile, after rain, the surface layers lose water by evaporation and transpiration, so the field capacity values that obtained after several days do not

Kramer [55] states that FWC will depend on soil temperature, that is, soil moisture in FWC will decrease as the soil temperature rises. Kirkham et al. [56] cite the influence of groundwater level, soil moisture depth, and impermeable layers in the soil on the FWC value. The author explains that the depth of soil moisture during infiltration will be greater the wetter the soil. Furthermore, the author states that the presence of an impermeable or less permeable soil layer increases the value of FWC. The equivalent of moisture according to Briggs and McLane [52] is the water constant obtained by centrifuging a soil sample with a force of thousand times greater than the gravitational force. The value roughly corresponds to the field capacity of the soil for water. The lentocapillary point (Lkt) was defined as the lower limit of optimal soil moisture and corresponds to a soil water pressure of 6.25 bar (pF = 3.8). It is obtained by subjecting a saturated fine to the specified pressure in the pressure membrane. The wilting point (Tv) is the equilibrium state between the suction force of the root system and the soil particles and plants starts to lose turgor. A pressure that occurs in soil depends on available water and for this hydropedological constant is 15 bar (pF = 4.2). The point of wilting can be determined by vegetation experiments, using a pressure membrane and calculate from hygroscopy. Plant-accessible water is in the range between the value of soil water capacity and the wilting point (**Figure 7**)

**Figure 6.** *Different water soil capacity.*

#### *Water Plant and Soil Relation under Stress Situations DOI: http://dx.doi.org/10.5772/intechopen.93528*

*Soil Moisture Importance*

with a volume of 100 cm3

Excess water in the soil causes problems in the plant's oxygen supply (occurrence of anoxia = complete lack of oxygen and occurrence of hypoxia = reduced amounts of oxygen). Anoxia occurs more often if the temperature 12°C of the air is above 20°C, when the consumption of oxygen by breathing the roots of plants, soil fauna, and microorganisms is higher than at lower temperatures. Under such anaerobic conditions or at insufficient oxygen concentration, changes in the metabolism of plant tissue cells occur. Cell intoxication with alcoholic fermentation products and increase in cytoplasm acidity occurs. These phenomena can result in cell death. Plants suffering from the lack of oxygen show signs of wilting, due to the inability to active transfer water, and the leaves show epinastic growth (downward) due to increased ethylene synthesis. In such leaves, the concentration of abscisic acid increased, which initiates the closure of the shoot. This interrupts the transpiration flow and distribution of osmolytes and water to up ground plant parts which resulting in growth retardation. The absolute soil water capacity according to Kopecky [53] corresponds to the water content in the micropores after complete saturation of the sample in a cylinder

after 24 hours. Horvat et al. [54] introduced the retention capacity of soil for water due to certain soil losses in determining the absolute capacity. According to this method, the soil sample in the cylinder, according to Kopecky [53] placed on a stand with filter papers whose edges immersed in water. The soil absorbs water and holds it in the micropores by adhesion, hydration, capillary, and surface tension forces. After squeezing, the excess water from the gravitational pores (the soil sample stands on the filter paper for half an hour) and the water content in volume % which corresponds to the retention capacity of the soil for water are is determined gravimetrically. The values of absolute and retention capacity of soil for water correspond to the soil layer above the groundwater level and are higher than those determined in field condition. Field water capacity (FWC) is a condition where micropores are filled with water and macropores with air, after maximum saturation and seepage of free water under the influence of gravity. Soil moisture at FWC is retaining longer provided there is no evaporation or the influence of groundwater (capillary). For field water capacity, there are many names such as retention capacity, maximum water capacity, capillary capacity, and water retention at 0.33 bar. However, this constant (FWC) is determined in field conditions, and therefore, the name filed water capacity is the most appropriate (**Figure 6**). Field water capacity is extremely important because

and squeezing of excess water from the soil macropores

**94**

**Figure 6.**

*Different water soil capacity.*

its knowledge used in various calculations in the design and use of hydromelioration systems. FWC is especially important for irrigation because it is water constant without is impossible to accurate calculate the irrigation rate to moisten the active rhizosphere. FWC is also the largest amount of water that can be giving during irrigation because water above the FWC value is considered harmful to the plant. Irrigation practice depends on soil conditions, moisture and plant's requirements. Field capacity corresponds to the state of moisture that occurs in the soil immediately after rain, before evaporation and transpiration begin. It is expressed as the percentage of water in the soil that is found in such a state of humidity. Therefore, it corresponds to the water content in the well-drained, permeable soil from which all the gravitational water had drained. However, soil moisture that would correspond to the absence of gravitational water alone must be determined relatively soon after rain. This is possible only with light and well-drained soils, because in others, the process of rain infiltration through the ecological profile takes a long time, often several days. Meanwhile, after rain, the surface layers lose water by evaporation and transpiration, so the field capacity values that obtained after several days do not correspond to the actual water content of the soil.

Kramer [55] states that FWC will depend on soil temperature, that is, soil moisture in FWC will decrease as the soil temperature rises. Kirkham et al. [56] cite the influence of groundwater level, soil moisture depth, and impermeable layers in the soil on the FWC value. The author explains that the depth of soil moisture during infiltration will be greater the wetter the soil. Furthermore, the author states that the presence of an impermeable or less permeable soil layer increases the value of FWC.

The equivalent of moisture according to Briggs and McLane [52] is the water constant obtained by centrifuging a soil sample with a force of thousand times greater than the gravitational force. The value roughly corresponds to the field capacity of the soil for water. The lentocapillary point (Lkt) was defined as the lower limit of optimal soil moisture and corresponds to a soil water pressure of 6.25 bar (pF = 3.8). It is obtained by subjecting a saturated fine to the specified pressure in the pressure membrane. The wilting point (Tv) is the equilibrium state between the suction force of the root system and the soil particles and plants starts to lose turgor. A pressure that occurs in soil depends on available water and for this hydropedological constant is 15 bar (pF = 4.2). The point of wilting can be determined by vegetation experiments, using a pressure membrane and calculate from hygroscopy. Plant-accessible water is in the range between the value of soil water capacity and the wilting point (**Figure 7**)

**Figure 7.** *Philodendron in well turgid (left) and in less turgid condition (right).*

and called physiologically active water. Within this interval, not all water is equally accessible, so the soil should maintain a moisture state between the water capacity and the lentocapillary point, which corresponds to the optimal moisture interval.
