The analysis of calculation methods for optimal water regime of soil in root zone of agricultural crops is given. A number of studies carried out in the Russian Federation with spring wheat, potato, lupine, clover, maize resulted in establishing that maximum yield was achieved under differentiated watering of soil active layer according to phases of vegetation development. The optimal water regime of alfalfa for green feed (80 % FC in the soil active layer (0–100 cm) is provided by conducting 4–5 vegetative irrigations depending on the weather conditions, while the yield increase of green mass was 46.25 ton per hectare comparing with no-irrigation variant. The results of research with maize and amaranth showed that there was no considerable decreasing of soil moisture indicators when the irrigation rate was reduced by 30 % comparing with the optimal one. For the greater part of active vegetation period for maize and amaranth soil moisture was at the level of 80 % FC in 0.7 m layer, but for pre-irrigation periods it decreased to 75 % FC. The research conducted to study water regime in the active layer of fodder crops made it possible to establish that under conditions of objectively limited water resources it is possible to decrease irrigation rates by 30 % and in the case of exigency – even by 50 %. It should be noted, however, that 30 % decrease in irrigation rates results in decrease of green mass yield for fodder crops by 10–15 % and 50 % decrease in irrigation rates results in 20–25 % decrease in green mass.
Keywords: soil water regime, crops, yield, irrigation rate, soil active layer, moisture, irrigation, phases of vegetation development, productivity of irrigated hectare.
