SOIL AND CLIMATIC SUBSATNTIATION OF SOYBEAN IRRIGATION SCHEDULES IN THE PRIALEYSKAYA STEPPE
The research was conducted on secondary meadow-chernozem soils formed due to the prairiefication of the southern chernozems. They are found under the conditions of natural drainage deterioration. In terms of humus horizon depth, they are medium deep soils (0.52-0.54 m) while regarding to humus content they are low-humic or oligohumic soils (2.9-3.8%). According to their hydrophysical and agrochemical properties, these soils are good for soybean cultivation. The climate of the district under study (The Prialeyskaya Steppe, the Aleysk Irrigation System) is similar to the climate of the other steppe districts of the Region. The average yearly air temperature is +1.6°С, the accumulated daily mean air temperature above +10°С amounts to 2342°С. The annual precipitation with the availability level of 50% is 449 mm, and during the growing season - 205 mm. the precipitation ratio (the ratio of the precipitation amount to evaporation) during the growing season makes 0.3; i.e. the precipitation amount meets the demand to 30-40% only. The hydrothermal index was 0.5 in 2016; 0.9 - in 2017 and 0.7 - in 2018. In 2016, the precipitation amount was 101.8 mm while the standard is 205.0 mm and at the same time the air temperature exceeded the standard by 1.5°С. In 2017, the precipitation amount was the same as on the previous years but the air temperatures were higher than the average yearly temperature by 1.2°С. The growing season of 2018 was dry and warm. In the period from May to September, the precipitation amount was 61.2 mm, or by 30% less than the standard, and the air temperatures were higher than the average yearly temperature by 1.6°С. The climatic conditions do not allow getting sustainable and high yields of soybeans without irrigation.