Reserves of humus substances in agrochernozem when cultivating sandy sainfoin

The results of a field experiment on the study of the humus state of agrochernozem are presented. The reserves of humic substances in agrochernozem were studied in the fields of a grain-fallow crop rotation and two grain-grass crop rotations. Soil tillage, sowing dates, seeding rate corresponded to zonal technologies. Means of intensification (mineral fertilizers, plant protection products) were not used. It is shown that the functioning of crop rotations with grain crops saturation and the cultivation of sainfoin under the cover of barley and in open crops caused a different accumulation of humus reserves. Sandy sainfoin, cultivated under the cover of barley, determined the replenishment of the relative reserves of total humus carbon in 0-40 cm thick soil by an average of 4% (108 t/ha). Quantitative estimates of the pool of water-soluble humus in the agrochernozem of binary crops of sainfoin of the second year of life exceeded the fallow field by 0.04-0.13 t/ha. In coverless crops of sainfoin, the replenishment amounted to 0.14-0.15 t/ha. The relative increase in water-soluble humus compounds in the 0-40 cm thick soil compared to the grain-fallow crop rotation was 21-36%. It has been established that most of the reserves of humic substances are accumulated in the subsurface layer of agrochernozem (20-40 cm), which is caused by their mineralization losses due to intensive cultivation (old arable soil) and losses due to deflation. Replenishment of moisture reserves in the soil contributed to an increase in the mineralization of humus and a decrease in its amount in the soil (r = -0.49...-0.68). The course of the seasonal dynamics of water-soluble humus in the 0-20 cm layer of agrochernozem under single and binary crops of sainfoin was positively (by 53-66%) associated with soil moisture.