CROP ROTATIONS ENSURING THE GREATEST YIELDS UNDER DRY CONDITIONS OF THE LOWER VOLGA REGION WATER-SAVING IRRIGATION REGIMES FOR VEGETABLE CROP PRODUCTION UNDER CONDITIONS OF VOLGA-DON INTERFLUVE

An estimation of various agro-biological methods in crop rotation of dry-steppe zone of light chestnut soils of the Lower Volga region is given. The effectiveness of a grain-fallow four-field crop rotation has been established, where green manure crop mass of winter rye, straw and leaf-weed mass of crops are plowed in soil, which increases organic matter and nutrient content in soil, reduces humus loss, and stabilizes grain yields. It was noted that only in four-field grain-fallow green manure crop rotation there is a positive balance of the main nutrients in the soil per hectare, where additional organic matter enters arable layer of soil in the form of winter rye green manure crop. In this variant, the balance was: nitrogen +39.7; phosphorus +0.7 and potassium +49.9 kg/ha. In six-field grain crop rotation with ginger as a sidereal crop, a positive balance is achieved only for phosphorus +14.1 and potassium +35.5 kg/ha, for phosphorus there is a negative balance of -3.5 kg/ha. In the eight-field grain crop rotation with 50% of legume crops, a positive balance is achieved only for potassium, +29.8 kg/ha. The balance of humus can be regulated by the structure of areas, alternation of crops in field crop rotations, application of plant residues in the form of sidereal crops, straw, leaf-weed mass, decrease in the proportion of fallow and tilled crops in the structure of biotivated crop rotations. The most complete biologization is possible in green manure crops, where humus losses decrease 1.5 times or more. A positive balance of organic matter is ensured in four-field biologized grain-fallow crop rotation - +3.33 t/ha.