The aim of the research is to substantiate the ecological rates of water demand for various types of soils for optimizing the meliorative state and soil fertility. The object of the research is various types of soils (gray forest, chernozem, chestnut, brown semidesert). Calculation of ecological standards of water demand of soils (ESWD) was carried out according to the coefficient of favorable ecological state of soils and landscapes. When calculating the average weighted biologically optimal irrigation rates (BOIR) that satisfy the needs of plants, the enlarged water requirements for irrigation of crops in the main federal districts were used for different soil types. As a result of the research, the calculated BOIR are offered for irrigation of agricultural crops. However, to optimize soil processes, it is necessary to create conditions close to natural ones which is possible with the establishment of ESWD, which for gray forest soils are equal to 60–63 mm, leached chernozems – 87–93 mm, typical chernozems – 104–120 mm, ordinary chernozems – 150–180 mm, southern chernozems – 200–250 mm, chestnut soils – 240–320 mm, brown desert-steppe soil – 380–550 mm. Thus, to obtain the planned yield, it is necessary to use BOIR for irrigation and ESWD show what amount of annual water loads can be used theoretically to create periodic natural conditions for soil formation, using irrigated and non-irrigated regimes in crop rotation. Moisture-loving crops with BOIR are cultivated in the irrigated regime, and in the non-irrigated regime, drought-resistant crops are grown without irrigation. In general, BOIR for crop rotation should be equal to ESWD. The ratio of irrigated and non-irrigated regimes in percent is 34:66 for gray forest soils, 37:63 for typical chernozems, 41:59 for ordinary chernozems in Central Black Earth Region (CBER), 49:51 for ordinary chernozems in Rostov region, 54:46 for southern chernozems; 67:33 for dark chestnut soils; 70:30 for light chestnut soils.
Keywords: optimal ecological standard, water demand, soil types, crop requirements, irrigation, soil formation conditions.
