The influence of grain-beet crop rotation with different leguminous predecessors of winter wheat on the nutritive regime of typical chernozem

In the upper soil layer (0-15 cm) there is a dependence of this index on rotation. A slightly higher amount of nitrogen was recorded in crop rotations with legumes, namely: with peas - 117 mg/kg soil, lathyrus - 114, soybeans - 118, and its highest content was in crop rotation with occupied vetch-oat mix fallow - 121 mg/kg soil. The increase in the content of this element in the soil, in our opinion, is due to the ability of legumes to accumulate it due to nitrogen fixation in the root system and crop residues. Studies have shown a decrease in the amount of nitrogen in crop rotation with corn for silage and fallow 110 and 111 mg/kg, respectively. In our opinion, in the crop rotation with fallow, less nitrogen was produced due to the absence of root and post-harvest residues during field breeding, and in the case of corn, a considerable amount of it was used to form a large amount of vegetated alienated mass.

The content of light hydrolysis nitrogen in the soil layer 15-30 cm did not exceed the values of the upper (0-15 cm) layer, which indicates the homogeneity of soil supply with this element. Despite the fact that the bulk of the root system of crops grown in the studied crop rotations is located in the arable layer of soil, this created favorable conditions for their development, especially in versions with legumes.

Comparison of our data on the content of light hydrolysis nitrogen in short-term rotations (1996-2009) with the initial data obtained during the laying of the experiment (1960) showed that the use of these rotations and the introduction of legumes did not worsen, and even improved soil nitrogen availability.

The availability of soil with mobile phosphorus is an indicator of its state of cultivation. With a lack of it in plants, the synthesis of proteins and carbohydrates is inhibited, there is a delay in growth and development and, as a result, their productivity decreases. Adequate plant nutrition with phosphorus accelerates the formation of reproductive organs, plant development and improves product quality. Crop phosphorus stocks are affected by crops, a crop rotation system, and a fertilizer system.

According to the results of our research, there was no clear dependence of this indicator on crop rotation. In the last 14 years of studies in the last crop rotation field, the amount of mobile phosphorus in the arable layer of soil, according to the existing estimate of its content, was increased and ranged from 122-137 mg/kg of soil (see Table 1). Moreover, the highest index of its content was in rotation with fallow 137 mg/kg of soil.

Better soil moisture conditions in the fallow version, lack of phosphorus removal by plants in this field, higher crop yields in crop rotation and, as a consequence, a greater number of crop residues that remained in the soil - all these factors, in our opinion, contributed to a noticeable increase in mobile forms in the soil. Chernozem soils are known to be well supplied with phosphorus. In addition, a significant part of it returns to the soil with plant debris in the process of their decomposition. The variant with the vetch-oat mix was approaching the fallow one by this indicator - 131 mg/kg. Vetch-oat mix before other predecessors of winter wheat frees up the field and this makes it possible to save moisture. In addition, the removal of phosphorus from the crop is reduced and the mobilization processes in the soil are improved due to the legume component, which helps to increase its content. Studies have shown a marked decrease in the content of mobile phosphorus in crop rotation, where the predecessors of winter wheat were legumes: peas, lathyru and soybeans. According to the obtained data, the amount of this element in the soil in these variants was 124, 122 and 122 mg/kg, respectively, due to the increased activity of microflora, which leads to its temporary fixation by microorganisms in organic form. Moreover, a large part of phosphorus imposed with harvest of crops. In crop rotation with corn for silage mobile phosphorus content amounted to 123 mg/kg soil. According to this indicator, crop rotation with corn is at the level of crop rotation with the legume component.

Studies have found an increase in the content of mobile phosphorus in the upper (0-15 cm) layer of soil in all crop rotations, which is due to the number of crop residues in this layer and the less intensive use of its root system of plants, which branches in the lower layer of soil. The content of mobile phosphorus retains the advantage of the fallow version over others.

Comparing the results obtained with the initial data from the stationary experiment, it should be noted that the content of mobile phosphorus in the arable layer of soil during the period of use of short-term crop rotations increased slightly.

Potassium plays an important role in crop production. It increases the winter and drought resistance of plants. Most researchers believe that its amount remains virtually unchanged depending on its predecessors. Other researchers believe that the use of fertilizers and crop rotation increases the level of supply of chernozem with potassium.

Studies have found an increase in the content of exchangeable potassium in the arable layer of soil in rotation with fallow. Its amount in the soil before barley harvest (fourth crop rotation field) was 131 mg/kg of soil, which is on average more than after other precursors of 14 mg/kg of soil. Moreover, in embodiments of precursors bean and corn for silage were almost equivalent data vary between 115-119 mg/kg soil.

Unlike nitrogen and phosphorus, black earth soils are known to be more enriched in potassium. The conversion of exchangeable potassium to a non-exchangeable form mostly occurs after the soil has dried up. Therefore, the high content of exchangeable potassium in both the top and bottom of the fallow variant, above all, can be attributed to the higher content of moisture in it. The advantage of fallow option over other crop rotations can also be explained by the lower removal of its plants. The higher content of exchangeable potassium in the upper (0-15 cm) of the arable layer in all crop rotations is probably due to the greater mass of crop residues in it and the movement of potassium from the lower horizons. In general, the content of exchangeable potassium in the soil can be classified as high, but far enough from the optimal values for typical chernozem. If, before the foundation of the experiment (1960), the arable layer of soil contained 271.9 mg/kg of soil, then by the end of the 11th rotation, its amount averaged 120 mg/kg of soil by rotation. That is, during the use of short-term crop rotations there is a decrease in the amount of potassium exchange in the soil. As for the amount of potassium in the upper and lower parts of the plow layer, we see a pattern similar to that of phosphorus.

Conclusions