NITROGEN-CARBON CIRCULATION IN AGROCENOSES WITH DIFFERENT FERTILIZATION SYSTEMS

The issue of transforming organic carbon, the dynamics, functions and regulation of fl ows in the soil-plant-atmosphere system at organic and intense fertilization system are urgent approaches of agrochemistry, and the increase in reserves of organic carbon, accessible for microorganisms, at different fertilization systems may be an effi cient way of optimizing nitrogen regime of chernozem due to optimization of balanced carbon-nitrogen interactions [1–5]. The shortage of active organic substance in soil is one of the reasons for low content of microbial biomass and poor recirculating activity of nitrogen at different fertilization systems, which is excluded from the circulation and removed from the agrocenosis [6–8]. Carbon is a relevant element of nutrition for agricultural crops, it is a component of soil organic substance – a natural source of supplying plants with mineral nutrition elements, it controls the processes of nitrogen-fi xation, denitrifi cation, mineralization and ISSN: 2312-3370, Agricultural Science and Practice, 2019, Vol. 6, No. 1


INTRODUCTION
The issue of transforming organic carbon, the dynamics, functions and regulation of fl ows in the soil-plant-atmosphere system at organic and intense fertilization system are urgent approaches of agrochemistry, and the increase in reserves of organic carbon, accessible for microorganisms, at different fertilization systems may be an effi cient way of optimizing nitrogen regime of chernozem due to optimi-zation of balanced carbon-nitrogen interactions [1][2][3][4][5]. The shortage of active organic substance in soil is one of the reasons for low content of microbial biomass and poor recirculating activity of nitrogen at different fertilization systems, which is excluded from the circulation and removed from the agrocenosis [6][7][8].
Carbon is a relevant element of nutrition for agricultural crops, it is a component of soil organic substance -a natural source of supplying plants with mineral nutrition elements, it controls the processes of nitrogen-fi xation, denitrifi cation, mineralization and NITROGEN-CARBON CIRCULATION IN AGROCENOSES WITH DIFFERENT FERTILIZATION SYSTEMS immobilization of nitrogen, and is a source of energy for microorganisms [9][10][11].
Fresh organic matter is the main limiting factor of mineral nutrition for agricultural crops, and thus is the foundation of optimizing properties and regimes of chernozem -a direct dependence between the content of organic carbon in soil and the volume of yield at different fertilization systems. Beyond the limits of critical (threshold) level of organic carbon content, the yield capacity does not depend on providing soil with organic matter [12][13][14][15][16][17][18][19].
The urgent issue is supporting a specifi c level of providing both the intense and organic systems of fertilization with organic carbon of potentially mineralizing organic matter, ensuring the equivalent amount of carbon of fresh organic matter with nitrogen, which is a key condition for harmonization of mineralizationimmobilization circulation of nitrogen in agrocenosis and removing the asynchrony between the formation of nitrogen in soil and its consumption [20][21][22][23]. The values of gross-and net-mineralized nitrogen in chernozem should correlate with the content of potentially mineralized (active) organic substance, thus, the value of balance capacity of organic carbon is a feature of the activity of nitrogen circulation in agrocenosis at different fertilization systems and formation of agrocenosis performance [24][25][26][27][28][29][30].
The aim of the study was to determine normative parameters of nitrogen-carbon circulation and comparative regularities of forming the performance of a short crop rotation with grain and intertilled crops at intense and organic systems of fertilization.

MATERIALS AND METHODS
The studies were conducted during a permanent fi eld experiment of the Cherkasy State Agricultural Experimental Station of the National Scientifi c Center "Institute of Agriculture", NAAS of Ukraine, established in 2010 on the area of 0.75 ha, the number of fi elds was 5, the area of seedling plot -30 sq.m., in four repeats.
The experiment was aimed at studying the crop rotation with cereals, grain legumes and technical crops: cereals -up to 60 % (winter wheat-spring barleycorn), grain legumes -up to 20 % (peas), technical crops -up to 20 % (soy).
The soil was podzolic heavily regraded low-humus medium-clay chernozem on carbonate forest layer. The humus content in the arable layer was 2.76-3.22 % according to I.V. Turin, the amount of absorbed alkali -24.5-28.1 mg-eq. per 100 g of soil, the hydrolytic acidity -1.99-2.19 mg-eq./100 g of soil, pH of the salt extract -6.0-7.1. The degree of saturation with alkali was 92.8-93.3 %, the content of mobile forms of phosphorus (according to Truog) -9.0 mg per 100 g of soil, exchange potassium (according to Brovkina) -12 mg per 100 g of soil.
The system of soil tillage in the crop rotation: surface tillage with diskers, subsurface tillage for the depth of ploughing and ploughing.
Two fertilization systems were studied in the experiment. The fi rst one -intense fertilization system (control variant) -envisaged the following doses of fertilizers: peas -N 30 P 50 K 50 ; winter wheat -N 30 P 90 K 90 + N 50 + N 40 ; soy -N 20 P 60 K 60 + N 40 ; corn -N 20 P 90 K 90 + N 100 ; spring barley -N 20 P 80 K 80. The second one -organic fertilization system (no mineral fertilizers: using by-products of the predecessor as an organic fertilizer, after treating grain with nitrogen-fi xing, phosphorusmobilizing biological preparations, growth regulators, humates and enriching with humates, growth regulators for plants or biopreparations).
The climate in the zone of studies is moderately continental. The average annual air temperature is +7.9 °С, the average monthly air temperature of the coldest month, January, is -5.9 °С, in July -+19.8 °С. Spring comes in the third decade of March. The notable specifi city of spring is an intense increase in temperature. No-frost period lasts 160-170 days. The sum of active temperatures during the period with the temperature above +10 °С is 2,650-2,900 °С. The total duration of the vegetation period is 200-210 days.
Balanced estimates of humus were conducted in accordance to the improved method of estimating humus balance in the projects of internal economic land utilization with the consideration of nitrogen removal with the main crop.
The estimation of the accumulation of carbon monoxide amount in a short crop rotation was performed on the following basis: ▪ yield of by-products, after-harvest residues and roots of crops in crop rotations according to the regression equations, presented for low and high levels of crop capacity, as the dependence of the number of plant residues is not always in proportion to the harvest increase; ▪ estimation of the yield of dry matter from the obtained mass; ▪ estimation of carbon content in the mass of byproducts, stubble and roots calculated into carbon oxide (coeffi cient 3.7); ▪ estimation of the amount of humus, which was formed as a reservoir of carbon depending on the level of the input of straw, by-products and mass of root system of plants into soil.
The generalization of materials and estimation of the study results was conducted by the method of disperse analysis and STATISTICA package with the non-parametric statistics.

RESULTS AND DISCUSSION
Mineral forms of nitrogen in the soil are accumulated due to mineralization of root extracts, plant remains, microbial biomass, humiс substances and by-products of decomposition of these organic substrates which, by the degree of availability of organic carbon, form an active pool of newly-formed organic substance, the decomposition of which occurs via activation of heterotrophic soil microorganisms, whose activity is regulated by the fertilization system [8].
The estimation of correlation coeffi cients demonstrated a direct strong correlation between the weight of the total phytomass and its constituents (R = +0.82--0.83 ± 0.02 R 2 = 0.67-0.69), and the correlation with the performance indices by the yield of fodder units was R = +0.86 ± 0.02 R 2 = 0.74. At the intense system of fertilization, a high level of correlation dependence (R = +>0.75) was found between the yield of the main product, the aboveground mass and quality indices of the main product. The correlations between the weight of the total phytomass, its constituents and quality indices of the main product were at the level of R = +0.59-0.74 ± 0.03, R = 0.35-0.55. The introduction of the organic fertilization system led to determining a direct correlation at the level of linear dependence between the weight of the total phytomass, its constituents and the quality of the main product: R = +0.98--0.99 ± 0.03, R 2 = 0.96-0.98.
At the intense fertilization system, the total reserves of N in the phytomass were 3.38 t/ha at the amplitude of 0.78 t/ha, and by the median the reserves of N in the phytomass exceeded the average value by 0.14 t/ha at the interval typical value of 0.68 t/ha. The value of N reserves by the median was closer to the upper typical value (3.68 t/ha). The variation coeffi cient was 10 %, and the approximation error was within the range of 5 %. The content of N in by-products was 1.09 t/ha with the amplitude of 0.82 t/ha (0.78-1.60 t/ha). By the median (Med 0..50 ), the content of N was at the level of the average value, and the typifi ed interval was 0.86--1.14 t/ha. The variation coeffi cient for nitrogen content exceeded 20 %, and the indices of asymmetry and excess had high positive values, which demonstrated high tempo of N accumulation in by-products. At the intense fertilization system, the reserves of N in the roots were 1.42 t/ha with the interval amplitude of 0.33 t/ha. The reserves of N by the median were close to the average value (1.46 t/ha) and the typifi ed amplitude was 0.13 t/ha. The variation coeffi cient was 8 %, and the approximation error was under 4 %.
At the organic system of fertilization, the content of N in the main products was 0.83 t/ha which was 1.19 times lower compared to the intense fertilization system, and the amplitude of the content of N was at the level of the intense fertilization system, but the mini-mal value of the content of N was 1.15 times lower. The content of N by the median was at the level of 0.80 t/ha which was 1.25 times lower compared to the intense fertilization system. The typifi ed (L 0.75 -L 0.25 ) amplitude was narrowed down to 0.16 t/ha, which was 2.06 times lower compared to the intense system of fertilization. The average reserves of N in the roots were at the level of the intense fertilization system (1.40 t/ha), and the amplitude (Δ = max-min) of the content of N was narrowed down 3 times due to the increase in the minimal value of the content of N 1.13 times to 1.33 t/ha. The typifi ed amplitude of the values of N content was narrowed down 33 times and was within the interval of the intense fertilization system. The variation coeffi cient for N content in the roots reached the level of 2.23 % which was 3.58 times lower compared to the control fertilization variant ( Table 1).
The total reserves of N at the organic fertilization system were 1.07 times lower compared to the intense fertilization system (3.15 t/ha) at the absolute interval amplitude of 0.55 t/ha. The reserves of N by the median were at the average value, but by the absolute value it was 1.13 times lower regarding the control fertilization system. Here the typical interval range of N reserves was narrowed down 4 times. The variation coeffi cient of N reserves in the crop rotation decreased 1.78 times, and the asymmetry coeffi cient was negative regarding the 1.13 times lower absolute value of the control fertilization system.
At the intense fertilization system, the intake of N was 0.403 t/ha at the amplitude of 0.361-0.435 t/ha (Δ = 0.074 t/ha). By the median, the intake of N was 0.420 t/ha at the typifi ed amplitude of 0.57 t/ha. The value of N intake by the median was closer to the upper typical value (L 0.75 = 0.425 t/ha), which demonstrated the increase in the amount of N in the crop rotation. The variation coeffi cient was 7.32 %, and the approximation error was under 4 %. At the organic system of fertilization, the average intake of N was 0.311 t/ha, which was 1.3 times lower, and the amplitude of the intake was narrowed down to 0.05 t/ha, which was 12 times lower compared to the intense fertilization system.
The normalized amplitude of the intake was narrowed down to the interval range of 0.310-0.319 t/ha which was 6.3 times lower by the amplitude compared to the intense fertilization system. The variation coeffi cient for N intake did not exceed 6 % and the approximation error was 2.5-3.0 %. At the intense fertilization system, the removal of N with the main products was 0.098 t/ha at the internal amplitude of 0.031 t/ha. By the median, the removal of nitrogen was close to the average value and the typifi ed interval coincided with the interval amplitude by the variation coeffi cient of 13.5 %. The coeffi cients of asymmetry and excess were negative with the considerable deviation of the latter from the distribution center (Table 2). At the organic system of fertilization, the average removal of N was 1.18 lower (0.083 t/ha) regarding the intense system of fertilization at the interval amplitude from 0.068 t/ha to 0.100 t/ha. The value of N removal by the median was 1.2 times lower compared to the 1.78-fold narrowed down typical interval amplitude (0.076-0.093 t/ha) regarding the control fertilization variant. The variation coeffi cient was 13 %, and the coeffi cients of asymmetry and excess had insignifi cant deviation from the distribution center. The removal of N due to humus mineralization at the intense fertilization system was 0.194 t/ha on average at the amplitude of 0.047 t/ha (0.0170-0.217 t/ha.) The value of N removal by the median was at the level of 0.203 t/ha, which was 4.5 % higher than the average value that was closer to the upper typical value of the removal (0.210 t/ha).
On average, the removal of N due to humus mineralization was 1.07 times lower regarding the intense system of fertilization at the absolute value of 0.182 t/ ha. The amplitude of N removal values was 1.24 times lower, amounting to 0.159-0.197 t/ha. The value of N removal by the median was 1.1 times lower and was getting closer to the average by the absolute value. The typical interval of N removal values was 6 times lower compared to the variation coeffi cient of 6.26 % which was 1.61-1.88 times lower compared to the intense system of fertilization. The asymmetry coeffi cient was negative, and it was 5 times higher which demonstrated intense retention of N removal due to humus mineralization. The removal of N due to humus mineralization at the intense fertilization system was 0.332 t/ha at the amplitude of 0.254 t/ha to 0.361 t/ha or 0.11 t/ha. The value of the total removal by the median was at the level of the average value of 0.336 t/ha at the normalized interval of values which was in the range of amplitude of 0.291-0.354 t/ha. The variation coeffi cient of the total removal of N was 12.3 % and the coeffi cients of asymmetry and excess had negative values and were getting to the center of the parameter distribution.
At the intense fertilization system, the balance of nitrogen was +0.081 t/ha at the amplitude from +0.054 to +0.117 t/ha. By the median the balance of N was at the level of +0.074 t/ha and the typifi ed amplitude of the balance of N was 0.068-0.102 t/ha. The value of the balance of N by the median was getting closer to the lower typical value. The variation coeffi cient was 25.4 %, and the coeffi cients of asymmetry and excess had insignifi cant deviation from the distribution center. At the organic system of fertilization, the balance of N in the crop rotation was positive, but 1.8 times lower by the absolute value regarding the intense fertilization system -0.045 t/ha. The absolute amplitude of the balance of N was 1.67 times lower and the interval values were also 2.25 and 1.9 times lower. The balance of N by the median was at the level of +0.048 t/ha which was 1.54 times lower compared to the intense fertilization system. The typifi ed parameters of the balance fl uctuated within the range of Δ = 0.030-0.057 t/ha which were 2.27 and 1.79 times lower. The variation coeffi cient increased 1.21 times and the values of asymmetry and excess of the distribution sampling were negative (left asymmetry), by the asymmetry they were getting closer to the distribution center, and it was considerable by the excess of deviation from the center by left asymmetry.
The capacity of nitrogen balance at the intense fertilization system for the crop rotation was 0.725 t/ha of nitrogen, and its amplitude fl uctuated from 0.621 to 0.796 t/ha with the amplitude of 0.175 t/ha N. The value of the nitrogen balance capacity by the median was 0.756 t/ha with the typical amplitude from 0.668 to 0.775 t/ha (Δ = +0.107 t/ha).
The value of nitrogen balance capacity was getting closer to the upper typical value (L 0.75 = 0.775 t/ha), which demonstrated the increase in the balance capacity. The variation coeffi cient of the balance capacity was 9.22 % and the coeffi cients of asymmetry and excess had negative values and a considerable deviation from the center of the sampling distribution. At the organic system of fertilization, the capacity of N balance on average for the crop rotation decreased 1.25 times regarding the intense system of fertilization, reaching 0.579 t/ha. The amplitude fl uctuated from 0.503 to 0.624 t/ha (+0.121 t/ha), which was 1.5 times lower compared to the control variant of fertilization. The value of N balance capacity by the median regarding the intense system of fertilization decreased 1.3 times and was getting closer to the average value (0.582 t/ha). The typical interval of values of N balance capacity fl uctuated within a smaller interval of values (0.579-0.600 t/ha) and the typifi ed amplitude regarding the intense system of fertilization was 5.1 times lower. The variation coeffi cient was 6.4 % which was 1.44 times lower regarding the intense system of fertilization. The asymmetry coeffi cient was negative which demonstrated the stability of forming the capacity of N balance under organic fertilization system.
The yield of fodder units in a short crop rotation with grain and intertilled crops in 2011-2018 from the capacity of balance and nitrogen content in the main products demonstrated that at the intense system of fertilization the dependence was of parabolic-plane nature, and the maximal performance (> 8.0 t/ ha) was noted for the capacity of nitrogen balance in the interval range of 640-750 kg, which ensured nitrogen accumulation in the main products at the level of 100-115 kg/ha. At the organic system of fertilization, the dependence of the increase in the yield of fodder units in a short crop rotation with grain and intertilled crops was of linear plane nature which was related to the 1.18-1.25-fold decrease in the performance regarding the intense system of fertilization (Fig. 1).
Supporting a specifi c level of soil provision with potentially mineralized carbon is a relevant prerequisite of including mineral nitrogen of soil into subsurface immobilization-remineralization circulation which is extremely important both for intense and organic fertilization systems.
Here the dynamics of mineralization-immobilization of nitrogen in soil depends on the ability to mineralize organic substrates and conditions, controlling remineralization of previously immobilized nitrogen, rather than on the total content of carbon and nitrogen in fresh organic substance [19]. At the intense fertilization system, the ratio of the content of organic carbon in the components of total phytomass was as follows: carbon of the main product : by-product : root mass =1 to 3.0 to 2.42, which was -15.6, 46.5, 37.9 % in percentage ratio. The average content of organic carbon in the main products was 1.92 t/ha at the amplitude range from 1.52 to 2.21 t/ha (0.69 t/ha). The variation coeffi cient for organic carbon in the main product was 14.1 % and the coeffi cients of asymmetry and excess had negative values.
The variation coeffi cient of organic carbon in the main product was 1.18-fold lower, reaching the values of 11.9 % and the coeffi cients of asymmetry and excess fl uctuated inconsiderably regarding the distribution center which demonstrated the stabilization of the emission of organic carbon in the main products during the period of investigating different systems of fertilization for chernozem.
The reserves of organic carbon in by-products at the intense fertilization system reached 5.76 t/ha with the amplitude from 5.11 to 6.31 t/ha. The typifi ed quarterly amplitude was 1 t/ha (Δ = 5.21-6.21 t/ha). The variation coeffi cient was 10 % lower and the coeffi cients of asymmetry and excess were negative, which demonstrated left asymmetry and the dynamic nature of carbon accumulation in by-products.
The accumulation of organic carbon in the root system at the intense fertilization system was at the level of 4.56 t/ha and the amplitude was 1.3 t/ha (3.61--4.91 t/ha). By the median, the reserve of carbon in the roots was closer to the typical value of the reserves (L 0.75 = 4.92 t/ha) at the typical interval of Δ = 0.31 t/ha. The variation coeffi cient was under 10 %, and the coeffi cients of asymmetry and excess had high values, which demonstrated the dynamic change in carbon reserves in the roots ( Table 3).
The systematic application of the organic system of fertilization led to the 1.09-fold decrease in the reserves of organic carbon in the by-products regarding the intense system of fertilization, and the amplitude was narrowed down 1.48 times and fl uctuated from 5.00 to 5.81 t/ha (+0.81 t/ha). By the median, the reserves of carbon in by-products were mostly getting closer to the minimal typical value (L 0.25 =5 .00 t/ha), and the typical amplitude of the index was twice lower. The variation coeffi cient decreased 1.45 times and the coeffi cients of asymmetry and excess were positive and had right asymmetry, which demonstrated the stabilization of directing the processes of carbon accumulation in the by-products at the organic system of fertilization. The organic fertilization system led to the decrease in carbon reserves in the phytomass down to 11.3 t/ha which was 1.09 times lower compared to the intense system of fertilization.
Narrowing down the amplitude of organic carbon reserves 1.72 times was revealed due to the 1.08-fold decrease in the reserves by the maximal value during the investigation years. Carbon reserves by the median were getting closer to the reserve values at average measurements, but regarding the control system of fertilization the reserves of carbon decreased 1.13 times, and the typical amplitude of the reserves -1.9 times, the variation coeffi cient was found to be under 5 % which was 1.78 times lower compared to the intense fertilization system.
While applying the organic fertilization system, the humifi cation process for organic carbon of plant remains and by-products by average and median values was slowed down 1.05-1.06 times and the typifi ed amplitude of organic carbon humifi cation regarding the amplitude decreased 5.37 times. The variation coefficient amounted to 6.68 %, and the coeffi cients of asymmetry and excess were positive, similar to the intense fertilization system, which characterized high intensity of the direction of carbon humifi cation of plant residues, but at a lower quantitative level due to decreased intake of organic mass prior to humifi cation. At the intense system of fertilization, the average capacity of organic carbon balance was 4.11 t/ha and by the median -4.16 t/ha. The normative amplitude of balance capacity was 0.37 t/ha which was 19.3 times lower than the amplitude. The organic system of fertilization led to the 1.08-1.1-fold decrease in balance capacity by the average and median values regarding the intense system of fertilization. The balance capacity by the median was getting closer to the minimal typical value (L 0.25 = 3.79 t/ha), and the normalized amplitude regarding the intense system of fertilization decreased 2.06 times. The variation coeffi cient was at the level of 5 %, and the coeffi cients of asymmetry and excess were positive at high absolute values.
Carbon balance at the intense fertilization system was positive (B = +0.57 t/ha), and the average value coincided with the balance value by the median. The amplitude of carbon balance was +0.61 t/ha and exceeded the normalized value 1.74 times. The variation coeffi cient of carbon balance was 40 % and the excess coeffi cient had a positive value and right asymmetry.
Despite of the detected regularity, the intensity of organic carbon balance was at a high level, regard-less of the fertilization system: the intense system of fertilization -126-136 %, and the organic system of fertilization -131-135 %. The variation coeffi cient of balance intensity at the organic system of fertilization did not exceed 5 %, and the coeffi cient of asymmetry of the sampling distribution was positive and had right asymmetry in the distribution of the sampling of values which demonstrated a stable increase in balance intensity towards activation.
The decomposition of fresh organic substance of the active pool occurred via the priority use of organic carbon by heterotrophic microorganisms which performed a structure-forming and energy-supplying function in metabolism. Microorganisms received the required amount of nitrogen from the organic substrate in the form of aminoacids or while consuming mineral forms of nitrogen from soil. Here the biomass of heterotrophic microfl ora had a narrower ratio of C:N compared to fresh organic substrate, consumed by them. It is diffi cult to determine in which way the conditions for capability to mineralization-immobilization of nitrogen of the organic substance are made up at different fertilization systems, and which conditions regulate the re-mineralization of previously immobilized nitrogen [25][26][27][28][29][30].
The statistical estimation of the ratio between organic carbon and N in the agrocenosis of a short crop rotation demonstrated that at the intense fertilization system, the average and median value of the ratio was 24 to 1, and the amplitude and normative amplitude was 22-27 to 1 and 22-24 to 1. The ratio of organic carbon to N by the median was getting closer to the upper typical value. The variation coeffi cient C to N in a crop rotation was 7.19 % and the asymmetry coeffi cient was positive and had right asymmetry with a considerable deviation from the center of sampling distribution. At the organic system of fertilization, the ratio of organic carbon to N in the agrocenosis of a short crop rotation by the average and median value reached 28 to 1, and the amplitude and typifi ed interval of values was 26-30 to 1 and 27-29 to 1. The typifi ed interval amplitude of the C to N ratio was narrower and the value of the ratio, which corresponded to the minimal and maximal typical state, were 1.22-fold higher compared to the intense fertilization system. The variation coefficient did not exceed 5 % and the asymmetry coeffi cient was positive.
The factor analysis allowed tracing the stability of correlations between the investigated parameters as well as between parameters and general factors, which carried the main diagnostic information about the processes in agrocenoses. The general model of nutrition demonstrated a strong reverse correlation between the main factor (F 1 ) -the yield of fodder units and the main products and the capacity of nitrogen balance (R = -0.90-0.96 ± 0.02; R 2 = 0.81-0.92), and the capacity of organic carbon correlated with factor F 2 at the level of a strong direct correlation (R = +0.96 ± 0.02; R 2 = 0.92). 70.0 % of total dispersion of factors accrued to factor F 1 , and F 2 -16.0 %. Two factors combine 86.0 % of dispersion. Determining the factor burden at the intense and organic fertilization systems by the abovementioned parameters was similar to the general model, but at the intense fertilization system, the distribution of total dispersion between factors was wider: F 1 = 67.0 %, F 2 = 24.0 %, and two factors combined 91.0 % of the total dispersion. At the organic system of fertilization, the distribution of dispersion corresponded to the general model of fertilization. The factor analysis allowed revealing the determining parameters of nutrition models, which were as follows: the yield of fodder units and the main products, the capacity of nitrogen balance and organic carbon. Direct and strong correlations were kept between the yield of fodder units and the content of organic carbon in the structural components of the total phytomass at the organic fertilization system: with organic carbon in the main product and the root mass: R = +0.86--0.88 ± 0.02; R 2 = 0.74-0.77, and with the content of carbon in the by-products and non-commodity total phytomass the relationship with the yield of fodder units was at the level of direct average correlation R = +0.58-0.65 ± 0.02, R 2 = 0.34-0.43; and the increase in the yield of fodder units was accompanied with the reverse correlation of the medium level: R = -0.64 ± 0.03; R 2 = 0.41. There were 0.28-0.29 units of carbon of the main product per one unit of the yield of fodder units, regardless of the fertilization system. Carbon of the by-products was spent 1.28-1.51 times, carbon of the roots -1.44, total non-commodity phytomass -1.28-1.94 times less compared to the general model and the model of intense system of fertilization. The increase in the yield of one fodder unit was accompanied with the 1.32-fold decrease in the capacity balance of carbon regarding the intense system of fertilization.
The capacity balance of nitrogen is a determining factor in the formation of high performance of agrocenosis, as it is subject to the capacity balance of carbon, the increase in which to the critical limit starts inhibiting the performance, which is related to the increase in the share of carbon capacity, which is accumulated by humus. At the intense system of fertilization the yield of fodder units up to 8.0-8.5 t/ha was accompanied with the increase in the capacity balance up to 4.0-4.6 t/ha, whereas at the organic system of fertilization, the yield of fodder units decreased to 7.5-8.0 t/ha which was accompanied with the increase in the capacity balance for carbon in which the share of organic carbon of humus increased regarding the intense system of fertilization, Fig. 2.

CONCLUSIONS
Direct and strong correlations were revealed between the yield of fodder units and the content of organic carbon in the structural components of the total phytomass at the organic fertilization system: with carbon in the main products and root mass -R=+0.86-0.88±0.02; R 2 =0.74-0.77, and with the content of carbon in byproducts and non-commodity total phytomass the relationship with the yield of fodder units was on the level of direct average correlation R=+0.58-0.65±0.02; R 2 =0.34-0.43. The increase in the yield of fodder units was accompanied with the 1.32-fold decrease in the capacity balance of carbon regarding the intense system of fertilization. At the organic system of fertilization, the ratio of organic carbon and nitrogen in the agrocenosis of a short crop rotation was the most optimal: 30 to 1, which was the most profi table for humifi cation of by-products and the decrease in the intensity of humus mineralization, which allowed reaching the positive values of the balance of organic balance at lower components of the balance items and a high level of balance intensity. Balance capacity was a restrictive factor in the circulation of carbon at the organic system of fertilization, which considerably conceded to the balance capacity of carbon at the intense fertilization system.
The performance of a short crop rotation with grain and intertilled crops was defi ned by the balance capacity of nitrogen and organic carbon and the content of these biogenic elements both in the main and total phytomass of crops in the rotation. At the intense fertilization system, the relationship between the yield of fodder units, the mass of the main products and the balance capacity of nitrogen, organic carbon and the content of these elements in the total phytomass had a parabolic character, and at the organic system -linearplane nature. The capacity of circulation nitrogen and organic carbon at the organic fertilization system and reserves of these biogenic elements in the total phytomass and the main products was 1.15-1.25 times lower compared to the intense system of fertilization, which was related to the 1.25-1.3-fold lower yield of the main products.

This article does not relate to any studies using humans and animals as investigation subjects.
Confl ict of interests. The authors deny any confl ict of interests.