Water consumption and irrigation regime of seed alfalfa under the conditions of regional climate change in the southern Steppe of Ukraine

The article presents the results of scientific research to specify the seed productivity of alfalfa grown on irrigated and rainfed lands of the southern Steppe of Ukraine. It is proved that obtaining stably high yields of conditioned alfalfa seeds under the conditions of regional climate change is possible only providing an optimal supply of productive moisture in the soil, since in recent years the crop has been grown under high temperature conditions and insufficient precipitation. It was established that irrigation of seed alfalfa throughout the growing season regardless of cultivar and mowing, should be conducted in two interphase periods: "the beginning of regrowth (shoots) – early budding" and "the beginning of budding – beginning of flowering". In the first interphase period, it is necessary to create conditions for optimal growth and development of plants that is achieved by maintaining the level of pre-irrigation humidity in 0-100 cm layer in the range of 70-75% MMHC on dark chestnut soils and 55-60% – on sandy loam chernozems. In the second interphase period, it is necessary to provide optimal conditions for the development of production processes and the formation of conditioned seed yields that is achieved by inhibiting growth processes, since alfalfa tends to grow up. Therefore, the level of pre-irrigation humidity of the calculated layer on medium and heavy loamy soils should be maintained within 60-65% MMHC and 45-50% MMHC – on sandy loam chernozems. The analysis of changes in natural and climatic conditions carried out over the past years shows that in the subzone of the southern Steppe, alfalfa cultivation for seeds is possible only by providing the developed irrigated agriculture. Getting the deficit of natural moisture solved, combined with high availability of heat resources and fertile dark‑chestnut soils and southern chernozems, is an objective natural prerequisite for further growth of seed productivity of alfalfa and reducing its dependence on extreme weather conditions and, above all, in medium‑dry (75%) and dry (95%) precipitation years.