Agrophysical properties of the soil depending on the crops of the grassland crop rotation

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Introduction
Currently, economically profitable crops occupy the main place in the structure of crop rotations of the Republic of North Ossetia-Alania: winter wheat in the steppe zone, corn for grain and partially potatoes in the foothill zone.The annual cultivation of these crops leads to a deterioration of the agrophysical properties of soils and to their depletion.Therefore, crop rotation must be designed, and not just organized and used [1][2].
Crop rotations are part of the farming system.In agronomy, crop rotations play a primary role among agrotechnical techniques.The culture of agriculture increases every year against the background of scientific application of mineral fertilizers, growth regulators, high-quality tillage, protection of plants from temporary exposure to pests, diseases, pests and weeds [3][4].
With proper alternation of crops, yields increase annually.The scientifically based structure of acreage is the basis of crop rotations.In crop rotations, in which row crops alternate with continuous sowing crops, a decrease in nitrates is associated with the consumption of their crops and the decomposition of their root system [5].
To a large extent, the agrophysical properties of the soil make up its fertility.The main indicator of soil condition is its density.Soil density affects the water, air, and thermal regimes of the soil, the intensity of microbiological processes in the soil, and ultimately yield [6][7].
The reason for low yields of agricultural crops is their cultivation on compacted soil, which depends on soil moisture, disturbances in the exchange of soil and atmospheric air, oxygen balance in the soil, which makes it difficult for the roots to breathe.With an increase in soil density, crop yields decrease due to a lack of oxygen in the soil and an excess of carbon dioxide.This decreases soil activity [8][9].
The physical condition of the soil is determined by the fact that, favorable water-air regime in the soil increases the development of microorganisms, which promote the absorption of nutrients and improve nutrition conditions for plants [10].
In this regard, an urgent task in modern agricultural production is the development of effective, highly productive crop rotations.

Materials and methods
The research was carried out in 2021-2023 in the field stationary crop rotation of the NCMPARI VSC RAS in the conditions of the forest-steppe zone of RNO-A.The soil of the experimental site is represented by chernozems leached on pebbles, characterized by a high content of gross and available reserves of nitrogen and phosphorus.In terms of the content of mobile potassium, they are moderately provided compared to other soils.The arable layer contains from 3.3% to 4.7% of humus.The reaction of the soil solution in the upper horizons is neutral.The annual precipitation rate is 748 mm.Their seasonal dynamics gradually increases from winter to summer, reaching a maximum in June (143 mm).In the future, precipitation decreases, reaching a minimum in December -February (20-27 mm).The relative humidity in the zone during the growing season is about 74%.
The experiment was placed by the method of organized repetitions, the experiment was repeated thrice, the options were placed by the method of trial plots, the shape of the plot is rectangular.The total area of the plot is 240 m 2 , the accounting area is 186 m 2 .
The laying of experiments, phenological observations, statistical processing of the obtained data will be carried out according to generally accepted methods described in the educational and methodological manual written by Adinyaev E.D., Abaeva A.A., Adaeva N.L. [11]; in the "Methodology of field experience" by Dospekhov B.A. [12].

Results and Discussion
In the forest-steppe zone of the RNO-Alania one has studied the influence of grassland crop rotation crops on the agrophysical, biological properties of the soil and crop productivity.One of the main morphological properties of the soil is its structure.It determines the state of the structure of the plowing layer, its aqueous, physico-mechanical and technological properties.The soil structure is determined by the interconnection of different sizes of soil aggregates.It is noted that the soil structure varies depending on the cultivation of crops.It was found that at the beginning of the growing season, the lumpy fraction under crop rotation crops varied from 13.34% to 49.45%, in the macrostructure -from 48.42% to 81.77%, on an aggregate 0.25 mm thick -from 1.77% to 7.99%.For corn (at the beginning of the growing season), the share of the lumpy fraction was 49.45%, by the end of the growing season this indicator decreased to 23.91%; the same tendency was observed for potatoes.A different picture has developed between clover and winter wheat: at the beginning of the growing season, the lumpy fraction amounted to 15.21 and 13.35%, by the end of the growing season it increased by 23.98 and 28.58%.At the end of the growing season, the proportion of the dusty fraction under winter wheat decreased from 7.96% to 1.05%, which was the lowest indicator.Among the crops: oats + clover and clover, this value was 3.52 and 3.76% at the end of the growing season and 6.87 and 2.69% at the beginning of the growing season.In potato plantings, the share of this fraction decreased from 4.30% to 3.89%.The dusty fraction on corn crops increased from 1.77% to 5.60.The structural coefficient ranged from 2.22% (corn) to 2.49% (oats + clover).
Continuous sowing crops (clover, winter wheat) had a positive effect on the soil structure, while row crops (corn, potatoes) were negatively evaluated in this regard.Surveys have shown that the studied soil has a good structure, since it contains from 46.0% to 66.2% of water-bearing aggregates.The volume weight, depending on the timing and depth of soil sampling, was different for the studied crops.The volume mass increased by the end of the growing season.The average soil density between all crops was optimal throughout the study period.On crops of oats + clover (on average 0-30 cm of soil layer), the soil density was 0.95 g/cm 3 at the beginning of the growing season, 1.19 g/cm 3 -during the period of intensive growth, 1.22 g/cm 3 -at the end of the growing season.This tendency is evident in all crops of crop rotation.It was found that the proportion of the solid phase during the growing season increases when sowing winter wheat and corn, which is explained by a change in soil density.At the beginning of the growing season, the general porosity is observed among crops: oats + clover (56.4%), clover (56.5%) and potatoes (57.7%), at the end of the growing seasonclover (56.0%) and potatoes (58.5%).On clover crops, the indicators of total porosity at the beginning of the growing season ranged from 41.3% to 41.4% and from 41.8% to 42.4%at the end.The level of capillary porosity among these crops ranged from 43.7% to 44.9%, at the beginning of the growing season -from 43.8% to 45.2%.It turned out that the capillary porosity increased from the beginning of the growing season to the middle period.This is due to the formation of the root system of plants, as well as surface tillage.Capillary porosity increased with depth, while non-capillary porosity decreased on the contrary.In general, the studied soil had an optimal phase ratio.
Studies of biological indicators of the fertility of leached chernozem have shown that the activity of cellulose decomposition is influenced by moisture, soil aeration, crop biology, mineral fertilizers, and features of agricultural technology (Figure 1).It was found that according to the scale evaluating the decomposition of cellulose, the intensity of decomposition of cellulose on leached chernozem is weak.The maximum loss of linen fabric during 90 days of exposure in all years of research was noted under row-crop plantings (potatoes -27.0%, corn -26.3%).Decomposition was less intense under clover crops of the second year of life -20.2%.
The final indicator determining the effectiveness of various field crop rotations is productivity of crops included in the crop rotation.The green mass of oats with clover was 21.4 t/ha, clover of the 2nd year of life -26.3t/ha, grain yield of winter wheat -3.9 t/ha, corn -5.9 t/ha and potatoes -26.7 t/ha.
It was found that the highest yield of food units was noted for corn -6.73 t/ha and potatoes -6.67 t/ha, on oat and clover crops, the collection of feed units amounted to 4.28 t/ha, clover -5.26 t/ha, winter wheat -4.97 t/ha.
It should be noted that rotation grass links are more productive, where food units harvesting (14.49t/ha) exceeds the indicators of the tilled crop link (13.4 t/ha).
In terms of the energy potential of cultivated crops and crop rotation link, the grassland had an advantage.The highest energy values in the grassland link of the crop rotation were for oats with clover -80.89MJ, clover 2 years of use -99.41 MJ, and in the tilled crop link for corn grain -24.19 MJ.In general, the energy value of the grassland link of the crop rotation turned out to be 206.62MJ more than the tilled one, and amounted to 245.08 MJ/ha.

Conclusion
It was found that in the studied crop rotation, perennial grasses and winter wheat have a positive effect on the soil structure, since they have a more powerful root system, with a longer growing season.Row crops (corn, potatoes) are noticeably inferior to them.
It was found that at the beginning of the growing season, the lumpy fraction under crop rotation crops varied from 13.34% to 49.45%, in the macrostructure -from 48.42% to 81.77%, on an aggregate 0.25 mm thick -from 1.77% to 7.99%.By the end of the growing season, the proportion of the silt fraction under winter wheat decreased from 8.01% to 1.09%.The structural coefficient ranged from 2.22% (corn) to 2.49% (oats + clover).Surveys have shown that the studied soil has a good structure, since it contains from 46.0% to 66.2% of water-stable aggregates.On crops of oats + clover (on average 0-30 cm of soil layer), the soil density was 0.95 g/cm 3 at the beginning of the growing season, 1.19 g/cm 3 during the period of intensive growth, 1.22 g/cm 3 -at the end of the growing season.This tendency is evident in all crops of crop rotation.It should be noted that rotation grass links are more productive, where food units harvesting (14.49t/ha) exceeds the indicators of the tilled crop link (13.4 t/ha).In general, the energy value of the grassland link of the crop rotation turned out to be 206.62MJ more than the tilled one, and amounted to 245.08 MJ/ha.

Fig. 1 .
Fig. 1.The effect of crop rotation crops on the biological activity of the soil in the foothill foreststeppe zone of the RNO-Alania.

Table 2 .
Productivity and energy efficiency of crop rotation crops in the foothill forest-steppe zone of the RNO-Alania.