**4. Primary productions and energy balance of permanent grassland**

Productivity of permanent grassland is a determinative component influencing affectivity of use of biomass, whether it involves fodder for ruminants or biomass for energy use. From the point of view of possibility of affecting productivity of permanent grasslands, it is necessary to understand that we are talking about open systems with many structures and functions, which are affected by many known and even larger number of unknown feedbacks. The site conditions (such as soil composition, supply of water) and the system of management that is being used have a huge impact on botanical composition and with it connected yield of biomass (Rychnovská & Parente, 1997).

Primary production of permanent grasslands is traditionally expressed in yield of dry matter (tDM ha-1). Variability in yield of permanent grassland is, considering different ecological conditions and different management, very broad and can vary in range of 1 – 15 (in rare cases even more) t ha-1.

As far as energy flows in ecosystem are concerned, it is more apposite to monitor the amount of produced energy from specific area of land. Expressing primary production of stands in energy units allows considering the suitability of applied management from the point of view of expressed energy inputs and outputs in the system. To calculate these balances the energy requirements of individual applied arrangements must be known and it is also necessary to determine the amount of energy contained in biomass.

#### **4.1 Calorific value**

174 Modeling and Optimization of Renewable Energy Systems

Water management – high infiltration of rainfalls and flood waters, maintenance of

 Function of biological filtration – they filter considerable amount of agents that are dangerous to health (nitrates, phosphates, biocides) and they prevent them from penetrating into deeper layers of the soil and subsequently into the underground water. Increasing soil fertility – they create large amount of dead organic matter and they

Health-hygienic function – production of oxygen, capturing of gas emission, reduction

Social economic function – particularly in marginal regions in connection with livestock

Permanent grasslands are able to fulfil these and other functions, provided that correct management is applied. Underutilized and neglected permanent grasslands are able to maintain these functions only in limited amount, or they can even contribute negatively in those areas, according many literal sources (Hopkins & Holz, 2006; Rychnovská, 1993; Rychnovská & Parente, 1997). Absence of regular utilization and grassland management cause degradation to fallow, and consequently, establishment of high number pioneer shrubs and trees. Planning of grassland management is necessary to conserve total diversity

Maintains of present status of grasslands and introduction of agro-environmental programs and agreements is one of the solution for sustainable development, it means the optimal and environmentally friendly utilization of nature resources like soil, water, plants and animals

Productivity of permanent grassland is a determinative component influencing affectivity of use of biomass, whether it involves fodder for ruminants or biomass for energy use. From the point of view of possibility of affecting productivity of permanent grasslands, it is necessary to understand that we are talking about open systems with many structures and functions, which are affected by many known and even larger number of unknown feedbacks. The site conditions (such as soil composition, supply of water) and the system of management that is being used have a huge impact on botanical composition and with it

Primary production of permanent grasslands is traditionally expressed in yield of dry matter (tDM ha-1). Variability in yield of permanent grassland is, considering different ecological conditions and different management, very broad and can vary in range of 1 – 15

**4. Primary productions and energy balance of permanent grassland** 

Protection and stabilization of biodiversity – plant and animal genetic resources.

Protection against erosion of soil – against both wind and water erosion.

Great supply of both above-ground and underground active living matter.

Balancing changes in temperature and humidity of surrounding air.

enrich the soil with humus, improving the soil structure.

Fixation of air nitrogen – both symbiotic and non-symbiotic.

breeding, they are used as source of living for people.

and retain its important functions in landscape (Moog et al., 2002).

connected yield of biomass (Rychnovská & Parente, 1997).

water reserves in the soil.

Aesthetic and landscape functions.

communities (Stypiński et al., 2009).

(in rare cases even more) t ha-1.

in dustiness and level of noise etc.

The amount of energy in biomass is possible to determine on the basis of calorimetric measurement. The principle of calorimetric determination of the volume of gross weight is based on burning down a sample in oxygen atmosphere and recording resulting increase of temperature in calorimetric system. The gross calorific value of the substance that is being burned down is counted using the following formula (1):

$$Q = \frac{\text{C.A.T} \cdot Q \mathbf{1}}{m} \tag{1}$$

Q – Gross calorific value of the sample (J g-1)

C – Heat capacity of the calorimeter system (J K-1)

Δ T – Increase in temperature of the calorimeter system during a combustion experiment (K)

Q1 – Extraneous energy from combustion of the cotton thread (J)

m – Mass of the sample (g)

It is possible to use acquired gross calorific value to determine other parameters, such as:


The usage of calorimetric method for studying plants has been already presented by Long (1934). The content of energy in plant material is given by the chemical composition in the plants and it can differ for individual plant species (Yajing et al., 2007). In mixed association, such as permanent grasslands, the content of energy is dependent on composition of species, but it can be changed during the vegetation (Neitzke, 2002). It depends on proportion of individual parts of plants (Sims & Singh, 1978), on ecological or climatic conditions (Long, 1934) and on other parameters.

As far as anthropogenic aspects are concerned, frequency of mowing and dosage of nutrients are considered to be the most important factors influencing the production of permanent grasslands. When appraising the significance of those as well as other ways of management on any of the indicators (the quality of the fodder, the content of energy in the fodder etc.), it is necessary to consider mainly experiments, where the chosen type of management is being applied on long-term basis. Permanent grasslands are dynamic associations, where stabilization occurs after long-term application of applied treatments. These experiments have higher testifying value then the short term ones.

Utilization of Permanent Grassland for Biogas Production 177

N0P0K0 N0P40K100 N50P40K100 N150P40K100 **Treatment: fertilization**

123 **Treatment: cutting**

Fig. 2. The effect of cutting sequence on calorific value (kJ g-1) of above-ground biomass of

permanent grassland, 2009, Černíkovice locality, Czech Republic

Fig. 1. The effect of fertilization on calorific value (kJ g-1) of above-ground biomass of

permanent grassland, 2009, Černíkovice locality, Czech Republic

16000

16000

16500

17000

17500

**kJ g-1**

18000

18500

19000

16500

17000

17500

**kJ g-1**

18000

18500

19000

The data presented below are results of long-term meadow experiments, where the dominant species was meadow foxtail (*Alopecurus pratensis*), alliance *Deschampsion cespitosae.* The experimental locality is situated near village Černíkovice, Czech Republic (49°46'26"N, 14°34'52"E), on alluvial meadow in 363 m a.s.l. Average annual rainfall is 664 mm, average annual temperature of locality is 7.2 °C. The soil type is Gleyic Fluvisol with level of underground water in range of 0.1 – 0.5 m under the surface.

The experiment with application of various doses of nutrients was started in 1966 and it is sorted by method of randomized blocks in four replications. The area of individual plots is 15 m2 (3 x 5 m). The stand is harvested in three subsequent cutting. There are six different treatments:


There was another experiment with different frequency of mowing found in 2001 at the same locality. The harvests are realized in May and in October for the two cuts per year treatment and in October for the one cut per year treatment. The monitored plots are not fertilized.

The samples of biomass for determination the content of energy were taken during vegetation period in years 2007 - 2009. The calorific value in the dry biomass was measured by the automatic adiabatic calorimeter system IKA C 5000 control. The calorific value was calculated according to the Czech State Standard ČSN ISO 1928 (1999), without the dissolving temperature of sulphuric acid and nitric acid correction.

Differences in calorific value in above-ground biomass of the permanent grassland according to supply of nutrients and sequence of cutting are presented in Fig. 1 and Fig. 2. Calorific value in above-ground biomass was, in average of three cuts, significantly influenced by treatment of fertilizing (*P = 0.0004),* where the lowest value (16891 J g-1) was recorded with the variant which was not fertilized and the highest value (18143 J g-1) with the variants fertilized by nitrogen. There was no proof of any significant influence of increasing the dosage of nitrogen. The content of energy in biomass differed in individual cuts (*P = 0.0053*). The highest one was in the first cut (18131 J g-1) and the lowest was in the third cut (17237 J g-1).

Although the presented results document significant effect of fertilization and cutting sequence on energy content in biomass, it is necessary to emphasize that the differences between minimal and maximal values range up to 10 %. This fact can be also noticed from results of another experiment in which permanent grassland that is cut once a year is compared with a different treatment cut twice a year. Significantly highest content of energy (*P = 0.0003*) in years 2007 – 2008 was recorded in biomass during spring harvest (18620 J g-1), and lowest (18006 J g-1) during autumn harvest of the twice cut treatment. Content of energy in biomass from treatment, which was cut once a year in autumn (18203 J g-1), did not differ from autumn harvest from treatment which was cut twice a year.

The data presented below are results of long-term meadow experiments, where the dominant species was meadow foxtail (*Alopecurus pratensis*), alliance *Deschampsion cespitosae.* The experimental locality is situated near village Černíkovice, Czech Republic (49°46'26"N, 14°34'52"E), on alluvial meadow in 363 m a.s.l. Average annual rainfall is 664 mm, average annual temperature of locality is 7.2 °C. The soil type is Gleyic Fluvisol with level of

The experiment with application of various doses of nutrients was started in 1966 and it is sorted by method of randomized blocks in four replications. The area of individual plots is 15 m2 (3 x 5 m). The stand is harvested in three subsequent cutting. There are six different

There was another experiment with different frequency of mowing found in 2001 at the same locality. The harvests are realized in May and in October for the two cuts per year treatment and in October for the one cut per year treatment. The monitored plots are not

The samples of biomass for determination the content of energy were taken during vegetation period in years 2007 - 2009. The calorific value in the dry biomass was measured by the automatic adiabatic calorimeter system IKA C 5000 control. The calorific value was calculated according to the Czech State Standard ČSN ISO 1928 (1999), without the

Differences in calorific value in above-ground biomass of the permanent grassland according to supply of nutrients and sequence of cutting are presented in Fig. 1 and Fig. 2. Calorific value in above-ground biomass was, in average of three cuts, significantly influenced by treatment of fertilizing (*P = 0.0004),* where the lowest value (16891 J g-1) was recorded with the variant which was not fertilized and the highest value (18143 J g-1) with the variants fertilized by nitrogen. There was no proof of any significant influence of increasing the dosage of nitrogen. The content of energy in biomass differed in individual cuts (*P = 0.0053*). The highest one was in the first cut (18131 J g-1) and the lowest was in the

Although the presented results document significant effect of fertilization and cutting sequence on energy content in biomass, it is necessary to emphasize that the differences between minimal and maximal values range up to 10 %. This fact can be also noticed from results of another experiment in which permanent grassland that is cut once a year is compared with a different treatment cut twice a year. Significantly highest content of energy (*P = 0.0003*) in years 2007 – 2008 was recorded in biomass during spring harvest (18620 J g-1), and lowest (18006 J g-1) during autumn harvest of the twice cut treatment. Content of energy in biomass from treatment, which was cut once a year in autumn (18203 J g-1), did not differ

underground water in range of 0.1 – 0.5 m under the surface.

N0P40K100 – application of 40 kg P ha-1 + 100 kg K ha-1 year-1

dissolving temperature of sulphuric acid and nitric acid correction.

from autumn harvest from treatment which was cut twice a year.

 N50P40K100 – application of 50 kg N ha-1 + PK N100P40K100 – application of 100 kg N ha-1 + PK N150P40K100 – application of 150 kg N ha-1 + PK N200P40K100 – application of 200 kg N ha-1 + PK

treatments:

fertilized.

third cut (17237 J g-1).

N0P0K0 – no fertilization

Fig. 1. The effect of fertilization on calorific value (kJ g-1) of above-ground biomass of permanent grassland, 2009, Černíkovice locality, Czech Republic

Fig. 2. The effect of cutting sequence on calorific value (kJ g-1) of above-ground biomass of permanent grassland, 2009, Černíkovice locality, Czech Republic

Utilization of Permanent Grassland for Biogas Production 179

produced during the year. The process of regeneration of growth can be significantly sped up by applying high dose of N-fertilizer (Frame, 2000). On the other hand, short intervals between individual cuttings lead to increased quality of harvested biomass. Plants in early phase of growth have lower content of fiber and higher content of proteins and watersoluble carbohydrates. This is favourable from the point of using biomass as a fodder or

Table 1 presents results of experiment with varying frequency of mowing from experimental location Nicov, Czech Republic. This stand of permanent grassland is located in 880 m a.s.l. (49°7'35.027"N, 13°37'0.435"E), on Loamy-sand type of soil. Long-term average of temperature is 6.0 °C, and long term average of rainfalls is 819 mm per year. The experiment was arrangement in the block design in three replications. The area of one plot is 18 m2 (1.5 x 12 m). Factors being monitored are various doses of nitrogen (40 kg N ha-1, 80 kg N ha-1 and variant without fertilization) and double frequency of mowing (two-cut and fourcut variant). The dose of 40 kg N ha-1 was applied on a one-time basis at the beginning of the vegetation period, dose of 80 kg N ha was divided into 40 kg N ha-1 at the beginning of the

**Number of cuts Fertilization 1st cut 2nd cut 3rd cut 4th cut Total yield (kg ha-1) (t ha-1)**  2 cuts N0P0K0 3.92 1.97 - - 5.89 N40P0K0 4.77 2.14 - - 6.91 N80P0K0 5.41 2.76 - - 8.17 4 cuts N0P0K0 2.68 1.44 1.23 0.40 5.76 N40P0K0 2.84 1.48 1.26 0.34 5.92 N80P0K0 3.16 1.90 1.44 0.39 6.89 Table 1. Effect of cutting and fertilization on biomass yields of permanent grassland (tDM ha-1),

There was no significant yield difference between two-cut and four-cut utilization in the locality of Nicov. Increasing size of doses of nitrogen led to an increase in yield in both variants of mowing, and to higher yield when using same dose of nitrogen were recorded when using the two-cut variant. These results show that the most suitable regime for mowing should come out of conditions of locality, as well as of the anticipated level of

From the result's listed in the Table 2, we can clearly see that one-cut variant used in the locality of Černíkovice is not compatible with the length of growth at the stand, and this represents significant loss in yield, or more precisely in energy, when compared to the two-

Frequency of mowing also affects yield of biomass in indirect way, through changes in botanical composition of the growth. In general, frequent mowing reduces presence of highgrowing species and supports increase in share of low-growing and shade-intolerant species, including leguminous species. Positive impact of leguminous species comes from their ability to assimilate aerial nitrogen with the help of rhizobia (Soussana & Tallec, 2010).

while the process of biogas formation.

vegetation period and 40 kg N ha-1 after first mowing.

average of years 2007 – 2009, Nicov locality, Czech Republic

fertilization (Table 1).

cut variant.

A difference in energy value of plants with different supply of nutrients was already recorded by Long (1934). Neitzke (2002) detected an influence of an increase in the nutrient supply on the calorific values only in some types of grasslands. On the contrary, Úlehlová (1980) while studying content of energy of permanent grasslands with low production of biomass, did not record any differences when using fertilization. The differences among weed species (*Elytrigia repens*, *Cirsium arvense*, *Chenopodium album*, *Amaranthus retroflexus*, *Echinochloa crus-galli*) recorded Fuksa et al. (2006). The calorific value of dry matter ranged from 16800 J g-1 (*A. retroflexus*) to 18210 J g-1 (*E. crus-galli*).

It is possible to conclude, that the change in content of energy in harvested biomass can be caused by change in chemical composition of plants within the species as a reaction to fertilization, and also by change of species composition of the vegetation. If the fertilization in a specific experiment has a low impact on composition of species or on increase of biomass in context of plants´ chemical composition, its impact will be also low as far as content of energy in plants is concerned. According to Fuksa et al. (2006) and Brant et al. (2011) it is necessary to replenish that calculation of energy produced from certain area of land is dependent primarily on yield of biomass, as content of energy in biomass has smaller variability then the yield. For precise calculation of energy balances, however, determining the content of energy in biomass is important.

#### **4.2 Factors affecting primary production of permanent grasslands**

Ability of yield of permanent grasslands is dependent on botanical composition, which is an outcome of interaction of stands´ conditions, competitive relationships among plants and a way of stand management. Composition of stand is usually affected the most by water and nutritional regime of the locality. Other edaphic, climatic and orographic factors, similarly to biotic factors (interaction with plants, animals and microorganisms) have lower impact in relation to botanical composition.

The most important agrotechnical intervention that can be used to affect primary production of permanent grasslands is regular cutting or pasture. The absence of management usually leads to degradation of grassland. Another important and very effective factor is fertilization. Other interventions (for example changes in water regime) are applied only on small areas, or they are not very effective in affecting yield (harrowing, dragging, rolling, additional seeding etc.).

#### **4.2.1 The impact of cutting on primary production**

While cutting, large part of assimilation area of plants is removed. Number of cuttings, date of mowing and the height of growth that is being mowed affects not only yield and quality of harvested matter, but also the ability of plants to regenerate for further growth.

High **frequency of cutting** has rather negative impact on yield of biomass, especially during the first half of vegetation period. The plants that are cut regenerate from nutrients stored in their root system. In residue of leaves and stalks there is still photosynthesis going on, however, because of small assimilation area, the production of carbonaceous agents is quite low. As a result the plants grow initially very slowly. However, with larger assimilation area also increases speed of growth. The more often plants reach this period, the less biomass is

A difference in energy value of plants with different supply of nutrients was already recorded by Long (1934). Neitzke (2002) detected an influence of an increase in the nutrient supply on the calorific values only in some types of grasslands. On the contrary, Úlehlová (1980) while studying content of energy of permanent grasslands with low production of biomass, did not record any differences when using fertilization. The differences among weed species (*Elytrigia repens*, *Cirsium arvense*, *Chenopodium album*, *Amaranthus retroflexus*, *Echinochloa crus-galli*) recorded Fuksa et al. (2006). The calorific value of dry matter ranged

It is possible to conclude, that the change in content of energy in harvested biomass can be caused by change in chemical composition of plants within the species as a reaction to fertilization, and also by change of species composition of the vegetation. If the fertilization in a specific experiment has a low impact on composition of species or on increase of biomass in context of plants´ chemical composition, its impact will be also low as far as content of energy in plants is concerned. According to Fuksa et al. (2006) and Brant et al. (2011) it is necessary to replenish that calculation of energy produced from certain area of land is dependent primarily on yield of biomass, as content of energy in biomass has smaller variability then the yield. For precise calculation of energy balances, however, determining

Ability of yield of permanent grasslands is dependent on botanical composition, which is an outcome of interaction of stands´ conditions, competitive relationships among plants and a way of stand management. Composition of stand is usually affected the most by water and nutritional regime of the locality. Other edaphic, climatic and orographic factors, similarly to biotic factors (interaction with plants, animals and microorganisms) have lower impact in

The most important agrotechnical intervention that can be used to affect primary production of permanent grasslands is regular cutting or pasture. The absence of management usually leads to degradation of grassland. Another important and very effective factor is fertilization. Other interventions (for example changes in water regime) are applied only on small areas, or they are not very effective in affecting yield (harrowing, dragging, rolling,

While cutting, large part of assimilation area of plants is removed. Number of cuttings, date of mowing and the height of growth that is being mowed affects not only yield and quality

High **frequency of cutting** has rather negative impact on yield of biomass, especially during the first half of vegetation period. The plants that are cut regenerate from nutrients stored in their root system. In residue of leaves and stalks there is still photosynthesis going on, however, because of small assimilation area, the production of carbonaceous agents is quite low. As a result the plants grow initially very slowly. However, with larger assimilation area also increases speed of growth. The more often plants reach this period, the less biomass is

of harvested matter, but also the ability of plants to regenerate for further growth.

from 16800 J g-1 (*A. retroflexus*) to 18210 J g-1 (*E. crus-galli*).

the content of energy in biomass is important.

**4.2.1 The impact of cutting on primary production** 

relation to botanical composition.

additional seeding etc.).

**4.2 Factors affecting primary production of permanent grasslands** 

produced during the year. The process of regeneration of growth can be significantly sped up by applying high dose of N-fertilizer (Frame, 2000). On the other hand, short intervals between individual cuttings lead to increased quality of harvested biomass. Plants in early phase of growth have lower content of fiber and higher content of proteins and watersoluble carbohydrates. This is favourable from the point of using biomass as a fodder or while the process of biogas formation.

Table 1 presents results of experiment with varying frequency of mowing from experimental location Nicov, Czech Republic. This stand of permanent grassland is located in 880 m a.s.l. (49°7'35.027"N, 13°37'0.435"E), on Loamy-sand type of soil. Long-term average of temperature is 6.0 °C, and long term average of rainfalls is 819 mm per year. The experiment was arrangement in the block design in three replications. The area of one plot is 18 m2 (1.5 x 12 m). Factors being monitored are various doses of nitrogen (40 kg N ha-1, 80 kg N ha-1 and variant without fertilization) and double frequency of mowing (two-cut and fourcut variant). The dose of 40 kg N ha-1 was applied on a one-time basis at the beginning of the vegetation period, dose of 80 kg N ha was divided into 40 kg N ha-1 at the beginning of the vegetation period and 40 kg N ha-1 after first mowing.


Table 1. Effect of cutting and fertilization on biomass yields of permanent grassland (tDM ha-1), average of years 2007 – 2009, Nicov locality, Czech Republic

There was no significant yield difference between two-cut and four-cut utilization in the locality of Nicov. Increasing size of doses of nitrogen led to an increase in yield in both variants of mowing, and to higher yield when using same dose of nitrogen were recorded when using the two-cut variant. These results show that the most suitable regime for mowing should come out of conditions of locality, as well as of the anticipated level of fertilization (Table 1).

From the result's listed in the Table 2, we can clearly see that one-cut variant used in the locality of Černíkovice is not compatible with the length of growth at the stand, and this represents significant loss in yield, or more precisely in energy, when compared to the twocut variant.

Frequency of mowing also affects yield of biomass in indirect way, through changes in botanical composition of the growth. In general, frequent mowing reduces presence of highgrowing species and supports increase in share of low-growing and shade-intolerant species, including leguminous species. Positive impact of leguminous species comes from their ability to assimilate aerial nitrogen with the help of rhizobia (Soussana & Tallec, 2010).

Utilization of Permanent Grassland for Biogas Production 181

(Lepš, 1999). Those are usually less valuable components of grasslands. Fertilization also supports creating of new tillers and larger foliage and in general it creates more robust

The effect of fertilization is usually bigger on swards that are less productive, but are composed of species which react well to fertilization. If favourable humidity conditions are present, it is possible with help of fertilization by mineral fertilizers to increase the yield by

Hopkins (2000) points out that at some localities, even if grasslands are based on very productive species (for example *Lolium perenne* and *Trifolium repens*), it is necessary to apply high doses of nutrients for maintaining of high yield, while original swards usually have

Source of production stability is high diversity of species in swards, whose auto-regulative mechanisms allow alternating dominance of group of species which are best adapted to

**Nitrogen** is considered to be the most important nutrient for increasing yield, but its overall effect has to be considered in more broad perspective. The response of sward to nitrogen fertilization was researched in many experiments all over the Europe. Most of grasslands were mowed at the same time, doses of N were ranging from zero to the extreme of 600 kg ha-1.The specific reaction of the sward is also dependent on other factors – the availability of water, weather of season, type of sward (content of leguminous species, density of grass shoots, the size of root system etc.), soil's characteristics, and frequency of defoliation

The increase of biomass when applying N is usually linear (15 – 25 kg of dry matter for 1 kg of N) up to doses of 250 – 350 kg ha-1. When applying higher doses of N (350 - 450 kg ha-1) the increase of yield drops down to 5 – 15 kg for 1 kg of applied N. Increase in yield stops at doses of 450 – 600 kg ha-1. When using mixture of grass and white clover, the yield increases in linear fashion up to 250 – 300 kg ha-1. The increases of biomass yield are lower, as clover gradually declines, until it disappears altogether and the grassland is then composed only of

Excessive input of nitrogen leads to undesired changes in vertical structure of growth, to mutual casting of shadow on leaves, to turning yellow of lower levels of sward and to reduction in photosynthesis. Natural fixation of nitrogen is stopped, unused nitrogen is leached into underground water and increased content of free nitrates in the plants

Annual individual nitrogen fertilization usually leads to initial increase in mass, but after several years the production decreases again as a result of exhaustion of other nutrients (Van Der Woude et al., 1994). At some localities the application of nitrogen does not have to produce any effect, because the growth of grassland is limited by different source (Malhi et al., 2010) – usually by phosphorus or potassium. Niinemets & Kull (2005) recorded significant increase in yield of grasslands on calcite soil even when phosphorus was applied solely. When phosphorus and calcium were applied in combination, the increase in yield

100 to 200 % as show for example Honsová et al. (2007).

much lower demands in this area.

climatic conditions of the particular year.

grass component (Frame, 2000; Whitehead, 1995).

was higher than when it was applied individually.

habitus of plants.

(Hopkins, 2000).

appears.

Changes in botanical composition have been described by number of authors. For example Kramerger & Gselman (1997) found that when using higher doses of N (180 kg ha-1) + PK, we can find in grasslands that are mowed often (6 times a year) more species, then in grasslands that are mowed only 2-3 times a year. Authors contribute this to competition over light between the plants. On the opposite, Zechmeister et al. (2003) describes negative correlation between richness of species variation and intensity of mowing. The highest amount of cuts that were included in the study, however, was 4 times a year. Level of fertilization was also lower.


Table 2. Effect of cutting (average of years 2007 – 2008, data in the upper part of the table) and effect of fertilization (2009, data in the lower part of the table) on biomass yield (tDM ha-1) and energy balance of permanent grassland, Černíkovice locality, Czech Republic

The optimal date for **first mowing** is from the beginning to full earing of the predominant grasses in the sward. Earlier mowing means increase of the quality and lower yield of fodder, later mowing results in the opposite (Frame, 2000). When we utilize early mowing, we support growth mainly of lower-growth species that are little affected by defoliation. When we utilize late mowing, there is decrease in quality of overgrown sod, which is felt the most in dry areas.

**Height of mowing** determines how much of assimilation area and reserve material is kept. Optimal height for mowing permanent grassland's is 30 – 40 mm. Lower height of mowing is more tolerable to creeping species (for example *Poa pratensis, Festuca rubra, Agrostis gigantea, Alopecurus pratensis*) than bunch type of grasses (*Dactylis glomerata, Phleum pratense, Festuca pratensis, Lolium perenne, Arrhenatherum elatius* etc.).

#### **4.2.2 Effect of fertilization on primary production**

Nutrients removed by harvest of permanent grasslands can be compensated for one part from soil's resources, for another part from the atmosphere (most importantly N) and also from application of fertilizers. The question of fertilizing permanent grasslands represents complex problem, which is composed of diversity and colorfulness of composition of swards in relationship to water and nutritional regime, the way sward is utilized, weather conditions, type of fertilizers, date and method of applying fertilizers etc.

Fertilizing supports development of species which have higher ability to use nutrients for creating a large amount of biomass and gain competitive advantage in this way. As a consequence plants of lower growth that reside in shade are eliminated from growth

Changes in botanical composition have been described by number of authors. For example Kramerger & Gselman (1997) found that when using higher doses of N (180 kg ha-1) + PK, we can find in grasslands that are mowed often (6 times a year) more species, then in grasslands that are mowed only 2-3 times a year. Authors contribute this to competition over light between the plants. On the opposite, Zechmeister et al. (2003) describes negative correlation between richness of species variation and intensity of mowing. The highest amount of cuts that were included in the study, however, was 4 times a year. Level of

**outputs** 

1 cut N0P0K0 4.80 87.38 1.58 85.77 55.19 2 cuts N0P0K0 7.91 145.39 2.81 142.58 51.66 3 cuts N0P0K0 6.08 102.97 3.11 99.86 33.13 N0P40K100 6.53 115.40 6.55 108.84 17.61 N50P40K100 8.56 154.51 11.34 143.17 13.63 N150P40K100 10.83 199.24 20.21 179.03 9.86 Table 2. Effect of cutting (average of years 2007 – 2008, data in the upper part of the table) and effect of fertilization (2009, data in the lower part of the table) on biomass yield (tDM ha-1)

and energy balance of permanent grassland, Černíkovice locality, Czech Republic

The optimal date for **first mowing** is from the beginning to full earing of the predominant grasses in the sward. Earlier mowing means increase of the quality and lower yield of fodder, later mowing results in the opposite (Frame, 2000). When we utilize early mowing, we support growth mainly of lower-growth species that are little affected by defoliation. When we utilize late mowing, there is decrease in quality of overgrown sod, which is felt the

**Height of mowing** determines how much of assimilation area and reserve material is kept. Optimal height for mowing permanent grassland's is 30 – 40 mm. Lower height of mowing is more tolerable to creeping species (for example *Poa pratensis, Festuca rubra, Agrostis gigantea, Alopecurus pratensis*) than bunch type of grasses (*Dactylis glomerata, Phleum pratense,* 

Nutrients removed by harvest of permanent grasslands can be compensated for one part from soil's resources, for another part from the atmosphere (most importantly N) and also from application of fertilizers. The question of fertilizing permanent grasslands represents complex problem, which is composed of diversity and colorfulness of composition of swards in relationship to water and nutritional regime, the way sward is utilized, weather

Fertilizing supports development of species which have higher ability to use nutrients for creating a large amount of biomass and gain competitive advantage in this way. As a consequence plants of lower growth that reside in shade are eliminated from growth

 **(kg ha-1) (t ha-1) (GJ ha-1) (GJ ha-1) (GJ ha-1) (GJ GJ-1)** 

**Energy inputs** 

**Energy gain** 

**Energy effectiveness** 

fertilization was also lower.

**of cuts Fertilization Yield Energy** 

*Festuca pratensis, Lolium perenne, Arrhenatherum elatius* etc.).

conditions, type of fertilizers, date and method of applying fertilizers etc.

**4.2.2 Effect of fertilization on primary production** 

**Number** 

most in dry areas.

(Lepš, 1999). Those are usually less valuable components of grasslands. Fertilization also supports creating of new tillers and larger foliage and in general it creates more robust habitus of plants.

The effect of fertilization is usually bigger on swards that are less productive, but are composed of species which react well to fertilization. If favourable humidity conditions are present, it is possible with help of fertilization by mineral fertilizers to increase the yield by 100 to 200 % as show for example Honsová et al. (2007).

Hopkins (2000) points out that at some localities, even if grasslands are based on very productive species (for example *Lolium perenne* and *Trifolium repens*), it is necessary to apply high doses of nutrients for maintaining of high yield, while original swards usually have much lower demands in this area.

Source of production stability is high diversity of species in swards, whose auto-regulative mechanisms allow alternating dominance of group of species which are best adapted to climatic conditions of the particular year.

**Nitrogen** is considered to be the most important nutrient for increasing yield, but its overall effect has to be considered in more broad perspective. The response of sward to nitrogen fertilization was researched in many experiments all over the Europe. Most of grasslands were mowed at the same time, doses of N were ranging from zero to the extreme of 600 kg ha-1.The specific reaction of the sward is also dependent on other factors – the availability of water, weather of season, type of sward (content of leguminous species, density of grass shoots, the size of root system etc.), soil's characteristics, and frequency of defoliation (Hopkins, 2000).

The increase of biomass when applying N is usually linear (15 – 25 kg of dry matter for 1 kg of N) up to doses of 250 – 350 kg ha-1. When applying higher doses of N (350 - 450 kg ha-1) the increase of yield drops down to 5 – 15 kg for 1 kg of applied N. Increase in yield stops at doses of 450 – 600 kg ha-1. When using mixture of grass and white clover, the yield increases in linear fashion up to 250 – 300 kg ha-1. The increases of biomass yield are lower, as clover gradually declines, until it disappears altogether and the grassland is then composed only of grass component (Frame, 2000; Whitehead, 1995).

Excessive input of nitrogen leads to undesired changes in vertical structure of growth, to mutual casting of shadow on leaves, to turning yellow of lower levels of sward and to reduction in photosynthesis. Natural fixation of nitrogen is stopped, unused nitrogen is leached into underground water and increased content of free nitrates in the plants appears.

Annual individual nitrogen fertilization usually leads to initial increase in mass, but after several years the production decreases again as a result of exhaustion of other nutrients (Van Der Woude et al., 1994). At some localities the application of nitrogen does not have to produce any effect, because the growth of grassland is limited by different source (Malhi et al., 2010) – usually by phosphorus or potassium. Niinemets & Kull (2005) recorded significant increase in yield of grasslands on calcite soil even when phosphorus was applied solely. When phosphorus and calcium were applied in combination, the increase in yield was higher than when it was applied individually.

Utilization of Permanent Grassland for Biogas Production 183

Fig. 3. Development of biomass yields (tDM ha-1) of permanent grassland in 1967 – 2006,

N0P0K0 2.66 2.54 0.88 6.08 N0P40K100 3.52 3.00 0.95 7.46 N50P40K100 4.64 3.00 0.97 8.62 N150P40K100 5.46 3.13 0.95 9.54

**Fertilization 1st cut 2nd cut 3rd cut Total yield** 

Table 3. Effect of fertilization on biomass yields of permanent grassland (tDM ha-1), average of

It is particularly important how high the yield was in relationship to the total production of energy that was determined for year 2009, which means that the calculated values were increasing proportionately to the increase in level of fertilization (Table 2). Highest values for the average of all variants of fertilization were recorded during first mow (67 GJ ha-1) and the lowest during third one (16 GJ ha-1). Total production of energy reached on these grasslands in Černíkovice (102.97 – 199.24 GJ ha-1) is comparable to total production of plants grown on arable soil. For example Fuksa et al. (2006) presented data on total energy production of silage maize in range from 107.27 to 231.04 GJ ha-1, depending on particular

Černíkovice locality, Czech Republic (Honsová et al., 2007)

years 2007 – 2009, Černíkovice locality, Czech Republic

**(kg ha-1) (t ha-1)** 

Impact of **phosphorus** on yield is, due to its low mobility, visible only after several years have passed. Its usage is increased when there is sufficient humidity and low reserve of available potassium in soil and it is dependent on botanical composition of the growth. Production effectiveness of P-fertilization is in average about 5.3 kg of dry matter to 1 kg of added P. With simultaneous application of K the production effectiveness increases to 22.5 kg of dry matter to 1 kg of added P (Klapp, 1956). The yield variability is usually higher then in sward that are not being fertilized, as a result of variations in cover by leguminous species. On soil with low content of P its influence can be supported by simultaneous Nfertilization (Frame, 2000).

**Potassium** is more mobile in soil then phosphorus and plants accept it easily. Its production effectiveness is lower then effectiveness of phosphorus. Klapp (1956) lists relative increase of yield by 12.5 %, and it increases throughout the years, as K-fertilization is continuously applied. The biggest effect is achieved on impoverished peat and peaty soils. To achieve good effect, it is important that sufficient humidity is present. Lack of K can be felt during dry years and particularly on stands with very low reserve of K in soil. In general, with insufficient potassium nutrition there is a reduction of photosynthesis, growth is slowed down, and there is a decrease in yield and quality of fodder, regardless of any potential Nfertilizing. There is a constraint in root system and together with decrease in effectiveness of regulating transpiration of leaves, the plant are more susceptible to dry weather (Frame, 2000).

The inaccessibility of phosphorus in soil for plants is often caused by too low level of pH. This can be improved by appropriate **liming**. Applying of calcium independently has only small effect on yield of biomass. It can cause only transitory mobilization of nutrients in soil, which leads to short-term increase in biomass yield. After exhausting all available nutrients, yield is reduced yet again. The increase in yield after liming varies within broad limits and is strongly dependent on placement and specific conditions (Klapp, 1956).

The effect of fertilization on above-ground biomass in permanent grassland is well visible in Fig. 3, which records long-term yields of four variants of fertilization used in experiment in Černíkovice. Yields were significantly affected by climatic conditions of the particular year. Lowest yields were always recorded in N0P0K0 variant, which was not fertilized. Yields from areas fertilized by PK started to show differences, from unfertilized areas, after approximately 25 years of periodical fertilization. Higher yields were recorded particularly in years that were favourable to growth of leguminous species. NPK-fertilizing, in most cases, significantly increased the yield. When 200 kg N ha-1 was applied, higher effect was recorded, in contrast with dose of 100 kg N ha-1.

In table 3 yields of biomass and production of energy of permanent grassland are shown which were evaluated from the same experiment in time period of 2007 – 2009. Total yield was significantly increasing as a result of applying nutrients: from 6.08 t ha-1 for nonfertilized variant to 9.67 t ha-1 for the variant N150P40K100. Significant effect of fertilization was recorded during monitored time period particularly during first mowing. It was not recorded in the course of following mows. This aspect can contribute to application of dose of nitrogen which happened before first mowing, which is also visible in share of first mowing on the total yield (44 – 57 %) rising proportionately to the dosage of fertilizer being applied.

Impact of **phosphorus** on yield is, due to its low mobility, visible only after several years have passed. Its usage is increased when there is sufficient humidity and low reserve of available potassium in soil and it is dependent on botanical composition of the growth. Production effectiveness of P-fertilization is in average about 5.3 kg of dry matter to 1 kg of added P. With simultaneous application of K the production effectiveness increases to 22.5 kg of dry matter to 1 kg of added P (Klapp, 1956). The yield variability is usually higher then in sward that are not being fertilized, as a result of variations in cover by leguminous species. On soil with low content of P its influence can be supported by simultaneous N-

**Potassium** is more mobile in soil then phosphorus and plants accept it easily. Its production effectiveness is lower then effectiveness of phosphorus. Klapp (1956) lists relative increase of yield by 12.5 %, and it increases throughout the years, as K-fertilization is continuously applied. The biggest effect is achieved on impoverished peat and peaty soils. To achieve good effect, it is important that sufficient humidity is present. Lack of K can be felt during dry years and particularly on stands with very low reserve of K in soil. In general, with insufficient potassium nutrition there is a reduction of photosynthesis, growth is slowed down, and there is a decrease in yield and quality of fodder, regardless of any potential Nfertilizing. There is a constraint in root system and together with decrease in effectiveness of regulating transpiration of leaves, the plant are more susceptible to dry weather (Frame,

The inaccessibility of phosphorus in soil for plants is often caused by too low level of pH. This can be improved by appropriate **liming**. Applying of calcium independently has only small effect on yield of biomass. It can cause only transitory mobilization of nutrients in soil, which leads to short-term increase in biomass yield. After exhausting all available nutrients, yield is reduced yet again. The increase in yield after liming varies within broad limits and

The effect of fertilization on above-ground biomass in permanent grassland is well visible in Fig. 3, which records long-term yields of four variants of fertilization used in experiment in Černíkovice. Yields were significantly affected by climatic conditions of the particular year. Lowest yields were always recorded in N0P0K0 variant, which was not fertilized. Yields from areas fertilized by PK started to show differences, from unfertilized areas, after approximately 25 years of periodical fertilization. Higher yields were recorded particularly in years that were favourable to growth of leguminous species. NPK-fertilizing, in most cases, significantly increased the yield. When 200 kg N ha-1 was applied, higher effect was

In table 3 yields of biomass and production of energy of permanent grassland are shown which were evaluated from the same experiment in time period of 2007 – 2009. Total yield was significantly increasing as a result of applying nutrients: from 6.08 t ha-1 for nonfertilized variant to 9.67 t ha-1 for the variant N150P40K100. Significant effect of fertilization was recorded during monitored time period particularly during first mowing. It was not recorded in the course of following mows. This aspect can contribute to application of dose of nitrogen which happened before first mowing, which is also visible in share of first mowing on the total yield (44 – 57 %) rising proportionately to the dosage of fertilizer being

is strongly dependent on placement and specific conditions (Klapp, 1956).

recorded, in contrast with dose of 100 kg N ha-1.

fertilization (Frame, 2000).

2000).

applied.

Fig. 3. Development of biomass yields (tDM ha-1) of permanent grassland in 1967 – 2006, Černíkovice locality, Czech Republic (Honsová et al., 2007)


Table 3. Effect of fertilization on biomass yields of permanent grassland (tDM ha-1), average of years 2007 – 2009, Černíkovice locality, Czech Republic

It is particularly important how high the yield was in relationship to the total production of energy that was determined for year 2009, which means that the calculated values were increasing proportionately to the increase in level of fertilization (Table 2). Highest values for the average of all variants of fertilization were recorded during first mow (67 GJ ha-1) and the lowest during third one (16 GJ ha-1). Total production of energy reached on these grasslands in Černíkovice (102.97 – 199.24 GJ ha-1) is comparable to total production of plants grown on arable soil. For example Fuksa et al. (2006) presented data on total energy production of silage maize in range from 107.27 to 231.04 GJ ha-1, depending on particular

Utilization of Permanent Grassland for Biogas Production 185

Negative effect of N-fertilization is a reduction of number of species in the sward. When the doses of nitrogen are increased, the number of species is reduced by 50 – 60 % (Willems et al., 1993; Zechmeister et al., 2003). N does not have to be the single factor affecting number of species, however. Permanent grasslands that are rich in species and are limited by N have about 30 – 40 species on area of 1 m2, swards limited by N and P can be even more rich in species. For example Niinemets & Kull (2005) recorded 70 – 90 species in area of 1 m2. Hejcman et al. (2007) found that many undemanding species that can spread in sward are fertilized solely by N, but when the PK-fertilization is added, they quickly start to decline. **Fertilization by phosphorus and potassium** has usually smaller effect on botanical composition of the sward, but it still has mostly positive effect. Its significance is higher on soils with lower content of available P and K. When PK-fertilizers are systematically applied, there is an increase in a share of legumes from average of 15 % for unfertilized swards up to 20 – 25 % (Klapp, 1956). At the same there is a decline in other dicotyledonous species (Mengel & Steffens, 1985). PK-fertilization also slightly increases a share of lower-

At some localities, P subsidiaries can negatively affect the number of species. Wassen et al. (2005) describes a case where limitation of N was more important then limitation of P. Enrichment of soil by phosphorus can lead to decline in species adapted to its low accessibility. Some of the more rare species can be suppressed that way and are often

Over fertilization by potassium leads significantly to negative effects. When extreme doses are applied and inappropriate ratio of N : P : K is used, it leads not only to decline of legumes, but later even grasses are forced out and ruderal weeds spread, such as *Rumex obtusifolius* etc. Shortage of K, on the other hand, reduces the ability of plants to survive winter. *Trifolium repens* is particularly sensitive to its shortage and it can result in a complete

Positive effect of P and K on the spread of legumes can be supported by suitable **application of Ca.** Ca itself has generally small effect on botanical composition of the growth. However when the pH is modified on acid soils, there can be suppression of some of the more

Conclusive **effect of variants** of fertilizing on botanical composition is shown on long-term fertilized grassland in Černíkovice. In the total evaluation of years 2007 – 2009 the variants of fertilization explained 21. 6 % of data variability. Ordination diagram (Fig. 4) shows the spread of intensity of fertilization along 1. axis (15.8 % of variation). The difference between unfertilized variant and PK variants and the variants that used N-fertilization is noticeable. Along the second axis there is a gradual increase in doses of applied N, which caused differences between botanical composition of N50P40K100 and N100P40K100 variants and the variants N150P40K100 and N200P40K100. Species that prospered on unfertilized and PK treatments were from monocotyledonous species, for example *Luzula campestris*, *Agrostis capillaris* and *Anthoxanthum odoratum*, furthermore all legumes (particularly *Lathyrus pratensis*), and number of other dicotyledonous species, for example *Alchemilla sp*. and genus *Ranunculus*. For variants N50P40K100 and N100P40K100, *Holcus lanatus* a *Deschampsia cespitosa* were dominant. For variants N150P40K100 and N200P40K100, high grass *Alopecurus pratensis* was dominant in the first place, and furthermore also *Urtica dioica* and *Elytrigia repens*. Analysis

growth and medium-growth grasses.

replaced by the more common species.

disappearance from the growth (Frame, 2000).

sensitive species.

year and the way growth was treated to improve its protection against weed. Rösch et al. (2009) set the production of energy from 66 GJ ha-1 (low-input grassland) to 119 GJ ha-1 (high-input grassland).

From the perspective of total energy balances (chapter 4.3) it is not only the total production of energy that is significant, but it is also important to consider necessary energy inputs, which are particularly high for nitrogenous fertilizers.

#### **4.2.3 The effect of fertilization on composition of species**

One of main factors affecting composition of species in grassland is the availability of nutrients, which is possible to significantly alter by usage of fertilizers (Hejcman et al., 2007). The most significant effect of fertilization is a direct influence on individual species, which will result in change of reciprocal abilities to compete. At the same time, indirect effect of nutrients will start, for example there will be increase in density of the sward, which leads to less light being able to penetrate into lower levels, which can provoke even more pressure to compete.

The number of species of plants has very close relationship to production of above-ground biomass (for example Hejcman et al., 2007; Oomes, 1992). On more impoverished localities, a number of low-growing species coexists. When the placement is gradually enriched by nutrients, the production of the above-ground biomass increases. At the same time, plants that are more demanding and higher are also able to spread and competition over light in the sward increases. Lower-growth species of plants disappear from grassland and only few species most capable in competition remain (Guo & Berry, 1998).

**N-fertilization** has the most profound effect in the starting period (3 – 6 years). It increases the cover of grasses (directly in proportion to the doses of N), mainly higher bunch and rhizomatic species. On oligothropic soils, the low grasses are replaced by medium-grown ones. At the same time, there is a significant decrease of cover of legumes – critical level of N doses, which can still maintain 10 – 15 % of legumes in meadows, is according to ecological conditions 50 – 60 kg ha-1. There is also a significant reduction in cover of other dicotyledonous species, particularly the lower ones (Mrkvička et al., 2006; Whitehead, 1995).

The following period is prominent for increase in cover of rhizomatic grasses, which gradually become the main part of the sward. The speed of their spread and size of the share of the sward they have is in direct proportion to dosages of N being applied (Honsová et al., 2007). Rhizomatic grasses have higher capacity of reserve organs, bigger leaf area left after mowing and higher ability of vegetative reproduction. Even though they are of lower growth, they are better adapted to applications of high doses of available N than bunch grasses are.

N fertilization not only significantly affects botanical composition, but its effect is also long-term. Systematic fertilization using higher doses of N (above 100 kg ha-1) gradually creates more simple, largely grass stands, and their grow shows higher dependence on meteorological conditions. This effect does not have to affect all localities, however, in some cases it is conditioned by adding PK-fertilization at the same time (Schellberg et al., 1999).

year and the way growth was treated to improve its protection against weed. Rösch et al. (2009) set the production of energy from 66 GJ ha-1 (low-input grassland) to 119 GJ ha-1

From the perspective of total energy balances (chapter 4.3) it is not only the total production of energy that is significant, but it is also important to consider necessary energy inputs,

One of main factors affecting composition of species in grassland is the availability of nutrients, which is possible to significantly alter by usage of fertilizers (Hejcman et al., 2007). The most significant effect of fertilization is a direct influence on individual species, which will result in change of reciprocal abilities to compete. At the same time, indirect effect of nutrients will start, for example there will be increase in density of the sward, which leads to less light being able to penetrate into lower levels, which can provoke even more pressure to

The number of species of plants has very close relationship to production of above-ground biomass (for example Hejcman et al., 2007; Oomes, 1992). On more impoverished localities, a number of low-growing species coexists. When the placement is gradually enriched by nutrients, the production of the above-ground biomass increases. At the same time, plants that are more demanding and higher are also able to spread and competition over light in the sward increases. Lower-growth species of plants disappear from grassland and only few

**N-fertilization** has the most profound effect in the starting period (3 – 6 years). It increases the cover of grasses (directly in proportion to the doses of N), mainly higher bunch and rhizomatic species. On oligothropic soils, the low grasses are replaced by medium-grown ones. At the same time, there is a significant decrease of cover of legumes – critical level of N doses, which can still maintain 10 – 15 % of legumes in meadows, is according to ecological conditions 50 – 60 kg ha-1. There is also a significant reduction in cover of other dicotyledonous species, particularly the lower ones (Mrkvička et al., 2006;

The following period is prominent for increase in cover of rhizomatic grasses, which gradually become the main part of the sward. The speed of their spread and size of the share of the sward they have is in direct proportion to dosages of N being applied (Honsová et al., 2007). Rhizomatic grasses have higher capacity of reserve organs, bigger leaf area left after mowing and higher ability of vegetative reproduction. Even though they are of lower growth, they are better adapted to applications of high doses of available N than bunch

N fertilization not only significantly affects botanical composition, but its effect is also long-term. Systematic fertilization using higher doses of N (above 100 kg ha-1) gradually creates more simple, largely grass stands, and their grow shows higher dependence on meteorological conditions. This effect does not have to affect all localities, however, in some cases it is conditioned by adding PK-fertilization at the same time (Schellberg et al.,

(high-input grassland).

compete.

Whitehead, 1995).

grasses are.

1999).

which are particularly high for nitrogenous fertilizers.

**4.2.3 The effect of fertilization on composition of species** 

species most capable in competition remain (Guo & Berry, 1998).

Negative effect of N-fertilization is a reduction of number of species in the sward. When the doses of nitrogen are increased, the number of species is reduced by 50 – 60 % (Willems et al., 1993; Zechmeister et al., 2003). N does not have to be the single factor affecting number of species, however. Permanent grasslands that are rich in species and are limited by N have about 30 – 40 species on area of 1 m2, swards limited by N and P can be even more rich in species. For example Niinemets & Kull (2005) recorded 70 – 90 species in area of 1 m2. Hejcman et al. (2007) found that many undemanding species that can spread in sward are fertilized solely by N, but when the PK-fertilization is added, they quickly start to decline.

**Fertilization by phosphorus and potassium** has usually smaller effect on botanical composition of the sward, but it still has mostly positive effect. Its significance is higher on soils with lower content of available P and K. When PK-fertilizers are systematically applied, there is an increase in a share of legumes from average of 15 % for unfertilized swards up to 20 – 25 % (Klapp, 1956). At the same there is a decline in other dicotyledonous species (Mengel & Steffens, 1985). PK-fertilization also slightly increases a share of lowergrowth and medium-growth grasses.

At some localities, P subsidiaries can negatively affect the number of species. Wassen et al. (2005) describes a case where limitation of N was more important then limitation of P. Enrichment of soil by phosphorus can lead to decline in species adapted to its low accessibility. Some of the more rare species can be suppressed that way and are often replaced by the more common species.

Over fertilization by potassium leads significantly to negative effects. When extreme doses are applied and inappropriate ratio of N : P : K is used, it leads not only to decline of legumes, but later even grasses are forced out and ruderal weeds spread, such as *Rumex obtusifolius* etc. Shortage of K, on the other hand, reduces the ability of plants to survive winter. *Trifolium repens* is particularly sensitive to its shortage and it can result in a complete disappearance from the growth (Frame, 2000).

Positive effect of P and K on the spread of legumes can be supported by suitable **application of Ca.** Ca itself has generally small effect on botanical composition of the growth. However when the pH is modified on acid soils, there can be suppression of some of the more sensitive species.

Conclusive **effect of variants** of fertilizing on botanical composition is shown on long-term fertilized grassland in Černíkovice. In the total evaluation of years 2007 – 2009 the variants of fertilization explained 21. 6 % of data variability. Ordination diagram (Fig. 4) shows the spread of intensity of fertilization along 1. axis (15.8 % of variation). The difference between unfertilized variant and PK variants and the variants that used N-fertilization is noticeable. Along the second axis there is a gradual increase in doses of applied N, which caused differences between botanical composition of N50P40K100 and N100P40K100 variants and the variants N150P40K100 and N200P40K100. Species that prospered on unfertilized and PK treatments were from monocotyledonous species, for example *Luzula campestris*, *Agrostis capillaris* and *Anthoxanthum odoratum*, furthermore all legumes (particularly *Lathyrus pratensis*), and number of other dicotyledonous species, for example *Alchemilla sp*. and genus *Ranunculus*. For variants N50P40K100 and N100P40K100, *Holcus lanatus* a *Deschampsia cespitosa* were dominant. For variants N150P40K100 and N200P40K100, high grass *Alopecurus pratensis* was dominant in the first place, and furthermore also *Urtica dioica* and *Elytrigia repens*. Analysis

Utilization of Permanent Grassland for Biogas Production 187

**Energy balance** of permanent grassland comes from comparison of inputs and outputs of energy. Energy outputs are divided into energy of plant production, residue of plants and irreversible energetic losses. For permanent grassland, the largest share is composed of above-ground biomass (industrially or alternatively usable biomass), as mentioned in

Input energy consists of energy of outer environment (sunlight, energy in soil, atmosphere and infrastructures of surround environment) and energy of technological inputs, which consist of direct part (energy of human work, fossil energy, other energy sources – draught animal etc.), and indirect part (energy of mechanisms, products of chemical industry, organic fertilizers, seeds etc.) (Hülsbergen et al., 2001). Additional energy can increase

Table 2 shows calculated energy inputs of permanent grassland with different levels of fertilization and frequency of mowing being applied, at the experimental location of Černikovice. Energy of human work, technological interventions (application of fertilizers, mowing and hay-making) and applied fertilizers were included in energy inputs. The largest share of inputs for the fertilized permanent grasslands is formed from energy in form of nitrogenous fertilizers. For grassland that is mowed three times a year, there was more then six times larger difference in the total value of energy inputs between unfertilized variant and the highest level of fertilization variant (N150P40K100). On the contrary, very low values were found for unfertilized grasslands that were harvested once

As is above-mentioned, total production of energy is dependent mainly on levels of yield reached, because the content of energy in biomass of permanent grassland has low variability. Assessment of energy balance further allows to evaluate total effectiveness of production of energy, when considering the same energy inputs into system. We calculated values of **energy gain** (difference between energy production and inputs of energy) and **energy effectiveness** (how much energy is produced from one unit of energy input) from the results of evaluation of experiments with different ways of managing grasslands in

From the evaluated energy balances follows that with the increase in level of fertilization, there is a significant increase of energetic gain (Table 2). For the N150P40K100 variant the energy gain was higher by 79.17 GJ ha-1 when compared to unfertilized variant. This difference was gained by increasing inputs from 3.11 to 20.21 GJ ha-1, which means by 17.10

In comparison to energy gain, highest values of energy effectiveness were reached in grassland with minimal inputs (no fertilization, low frequency of mowing). With the intensification of management (particularly fertilization), this value decreases. Energy effectiveness of crops grown on arable soil is according to findings of Hülsbergen et al. (2001) for example for potatoes 4.3, winter wheat 14.4, winter barley 9.4, spring barley 9.9 and sugar beets 11.1 GJ GJ-1. With the increase of additional energy inputs the energy effectiveness in permanent grasslands decreases, however it still reaches higher values in

volume of sunlight energy that is captured in biomass (Jones, 1989).

**4.3 Energy balance of permanent grassland** 

chapter 4.2.

or twice a year.

locality of Černíkovice.

comparison with crops grown on arable soil.

GJ ha-1.

of redundance (RDA) has also shown conclusive **effect of year** on botanical composition, which has explained 3.2 % of data variability.

Note: *Agrostis capillaris – AgroCap, Agrostis stolonifera – AgroSto, Achillea millefolium – AchiMil, Ajuga reptans – AjugRep, Alchemilla sp. – AlchSp, Alopecurus pratensis – AlopPra, Anthoxanthum odoratum – AnthOdo, Anthriscus sylvestris – AnthSyl, Cerastium holosteoides – CeraHol, Cirsium arvense – CirsArv, Cirsium palustre – CirsPal, Cirsium vulgare – CirsVul, Cynosurus cristatus – CynoCri, Dactylis glomerata – DactGlo, Deschampsia caespitosa – DescCes, Elytrigia repens – ElytRep, Equisetum palustre – EquiPal, Festuca pratensis – FestPra, Glechoma hederacea – GlecHed, Holcus lanatus –HolcLan, Lathyrus pratensis – LathPra, Luzula campestris – LuzuCam, Lysimachia nummularia – LysiNum, Plantago lanceolata – PlanLan, Poa pratensis – PoaPra, Poa trivialis – PoaTri, Ranunculus acris – RanuAcr, Ranunculus auricomus – RanuAuri, Ranunculus repen – RanuRep, Rumex acetosa – RumeAce, Stellaria graminea – StelGra, Taraxacum sect. Ruderalia – TaraSp, Trifolium dubium – TrifDub, Trifolium hybridum – TrifHyb, Trifolium repens – TrifRep, Trisetum flavescens – TrisFla, Urtica dioica – UrtiDio, Veronica arvensis – VeroArv, Veronica chamaedrys – VeroCha, Veronica serpyllifolia – VeroSer*

Fig. 4. RDA analysis of relationship between species composition of permanent grassland and variants of long term fertilization, average of years 2007 – 2009, Černíkovice locality, Czech Republic

Suitable management of permanent grasslands can lead to increase in diversity, although this usually has negative impact on production. Biodiversity has value not only from the point of ethical and esthetical view, but it also is important for preserving species and their genotypes, as the diversity of ecosystem leads to its stability (Nösberger & Kessler, 1997).

#### **4.3 Energy balance of permanent grassland**

186 Modeling and Optimization of Renewable Energy Systems

of redundance (RDA) has also shown conclusive **effect of year** on botanical composition,

*CynoCri*

*VeroCha*

5-8

*TrifDub*

*HolcLan FestPra*

3 4

*DescCes*

1 2

*12 AgroCap*

*1 DactGlo*

*2 VeroArv*

*3 TrisFla*

*4 CeraHol*

*5 PoaTri*

*6 CirsVul*

*7 VeroSer*

*9 TrifHyb 11 TrifRep*

*10 CirsPal*

*14 AnthOdo*

*13 AjugRep*

*LuzuCam*

*RumeAce*

*EquiPal*

*RanuAuri*

*AlchSp*

**N0P0K0**

*LathPra*

*LysiNum*

*TaraSp 8 StelGra*

**N0P40K100**

*RanuAcr*

11-13 14

*RanuRep*

*PlanLan*

9-10

*AchiMil*


Note: *Agrostis capillaris – AgroCap, Agrostis stolonifera – AgroSto, Achillea millefolium – AchiMil, Ajuga reptans – AjugRep, Alchemilla sp. – AlchSp, Alopecurus pratensis – AlopPra, Anthoxanthum odoratum – AnthOdo, Anthriscus sylvestris – AnthSyl, Cerastium holosteoides – CeraHol, Cirsium arvense – CirsArv, Cirsium palustre – CirsPal, Cirsium vulgare – CirsVul, Cynosurus cristatus – CynoCri, Dactylis glomerata – DactGlo, Deschampsia caespitosa – DescCes, Elytrigia repens – ElytRep, Equisetum palustre – EquiPal, Festuca pratensis – FestPra, Glechoma hederacea – GlecHed, Holcus lanatus –HolcLan, Lathyrus pratensis – LathPra, Luzula campestris – LuzuCam, Lysimachia nummularia – LysiNum, Plantago lanceolata – PlanLan, Poa pratensis – PoaPra, Poa trivialis – PoaTri, Ranunculus acris – RanuAcr, Ranunculus auricomus – RanuAuri, Ranunculus repen – RanuRep, Rumex acetosa – RumeAce, Stellaria graminea – StelGra, Taraxacum sect. Ruderalia – TaraSp, Trifolium dubium – TrifDub, Trifolium hybridum – TrifHyb, Trifolium repens – TrifRep, Trisetum flavescens – TrisFla, Urtica dioica – UrtiDio, Veronica arvensis – VeroArv, Veronica chamaedrys –* 

Fig. 4. RDA analysis of relationship between species composition of permanent grassland and variants of long term fertilization, average of years 2007 – 2009, Černíkovice locality,

Suitable management of permanent grasslands can lead to increase in diversity, although this usually has negative impact on production. Biodiversity has value not only from the point of ethical and esthetical view, but it also is important for preserving species and their genotypes, as the diversity of ecosystem leads to its stability (Nösberger & Kessler, 1997).

which has explained 3.2 % of data variability.

*AgroSto AlopPra*

*PoaPra*

**N150P40K100**

**N200P40K100**

*VeroCha, Veronica serpyllifolia – VeroSer*

*ElytRep*

*UrtiDio*

*GlecHed*

**N100P40K100**

*AnthSyl*

*CirsArv*

**N50P40K100**


Czech Republic

1.0

**Energy balance** of permanent grassland comes from comparison of inputs and outputs of energy. Energy outputs are divided into energy of plant production, residue of plants and irreversible energetic losses. For permanent grassland, the largest share is composed of above-ground biomass (industrially or alternatively usable biomass), as mentioned in chapter 4.2.

Input energy consists of energy of outer environment (sunlight, energy in soil, atmosphere and infrastructures of surround environment) and energy of technological inputs, which consist of direct part (energy of human work, fossil energy, other energy sources – draught animal etc.), and indirect part (energy of mechanisms, products of chemical industry, organic fertilizers, seeds etc.) (Hülsbergen et al., 2001). Additional energy can increase volume of sunlight energy that is captured in biomass (Jones, 1989).

Table 2 shows calculated energy inputs of permanent grassland with different levels of fertilization and frequency of mowing being applied, at the experimental location of Černikovice. Energy of human work, technological interventions (application of fertilizers, mowing and hay-making) and applied fertilizers were included in energy inputs. The largest share of inputs for the fertilized permanent grasslands is formed from energy in form of nitrogenous fertilizers. For grassland that is mowed three times a year, there was more then six times larger difference in the total value of energy inputs between unfertilized variant and the highest level of fertilization variant (N150P40K100). On the contrary, very low values were found for unfertilized grasslands that were harvested once or twice a year.

As is above-mentioned, total production of energy is dependent mainly on levels of yield reached, because the content of energy in biomass of permanent grassland has low variability. Assessment of energy balance further allows to evaluate total effectiveness of production of energy, when considering the same energy inputs into system. We calculated values of **energy gain** (difference between energy production and inputs of energy) and **energy effectiveness** (how much energy is produced from one unit of energy input) from the results of evaluation of experiments with different ways of managing grasslands in locality of Černíkovice.

From the evaluated energy balances follows that with the increase in level of fertilization, there is a significant increase of energetic gain (Table 2). For the N150P40K100 variant the energy gain was higher by 79.17 GJ ha-1 when compared to unfertilized variant. This difference was gained by increasing inputs from 3.11 to 20.21 GJ ha-1, which means by 17.10 GJ ha-1.

In comparison to energy gain, highest values of energy effectiveness were reached in grassland with minimal inputs (no fertilization, low frequency of mowing). With the intensification of management (particularly fertilization), this value decreases. Energy effectiveness of crops grown on arable soil is according to findings of Hülsbergen et al. (2001) for example for potatoes 4.3, winter wheat 14.4, winter barley 9.4, spring barley 9.9 and sugar beets 11.1 GJ GJ-1. With the increase of additional energy inputs the energy effectiveness in permanent grasslands decreases, however it still reaches higher values in comparison with crops grown on arable soil.

Utilization of Permanent Grassland for Biogas Production 189

first place starting potential for following degradation. Real yield of biogas from plant biomass is then affected mainly by technological parameters of the process of degradation, from the size of input particles, parallel fermentation of various substrates, to compliance

In the following sub-chapters 5.2 there are results of experiments with various types of management of permanent grasslands and the impact on yields of substrate and total

Assessment of yield of biogas from biomass represents basic qualitative characteristic in this process of energy production. As mentioned before, the basic thing is content of individual nutrients. This fact leads to logical effort to theoretically calculate production of biogas from its content. Amon et al. (2007) described the methane energy value model, which estimates methane yield from the nutrient composition of energy crops in mono fermentation via regression models. This model investigates and considers the impact of the content of crude protein, crude fat, crude fiber and N-free extracts on the methane formation. It is necessary to put a reminder here, however, that the calculations based on content of nutrients or laboratory tests of amount of yield described below, show potential degradation of biomass with ideal conditions present. As above-mentioned, real values reached depend on

Table 4 presents results of substrate biogas yield in litter per kg of dry matter (1 kg-1DM) from two experimental locations (Nicov and Černíkovice) in 2009. Characteristics of locality

**Locality Fertilization 1st cut 2nd cut 3rd cut 4th cut** 

**(kg ha-1) (l kg-1DM)** 

Nicov N0P0K0 318 380 - -

 N40P0K0 364 367 - - N80P0K0 338 317 - -

 N0P0K0 445 331 407 503 N40P0K0 358 425 453 445

N80P0K0 375 418 405 414

Černíkovice N0P0K0 520 410 541 - N50P40K100 545 484 483 -

N150P40K100 446 467 588 -

Table 4. Substrate biogas yield (l kg-1DM) from permanent grassland, 2009, Nicov and

Černíkovice localities, Czech Republic

conditions and design of these experiments are mentioned in chapters 4.1 and 4.2.

with suitable conditions for all levels of micro-bacterial degradation.

technological aspects of fermentation in a specific biogas plant.

production of biogas described.

**5.2 Substrate biogas yield** 

On the basis of the present results it can be concluded, that for swards with suitable botanical composition while the energy in form of fertilizers is added, it leads to adequate yield reaction and the value of energy gain reached is comparable with intensive crops on arable soil. In contrast to regular crops on arable soil, permanent grasslands reach noticeably higher levels of energy effectiveness as a result of very low energy inputs into system.
