The change of the humus content and agrochemical characteristics of leached chernozem under the prolonged usage of different tillage systems in oil crops rotation

In 1971-2011, the systems of primary tillage (intensive, plowing at a different depth, minimal and surface) in oil crops rotation (sunflower, castor, soybean, winter and spring rapeseed) were studied in a VNIIMK stationary experiment in 4 rotations of ten-field grain-tilled crop rotation. In the first rotation it was noted that the total amount of nutrients in plow layer of soil was similar under intensive, minimal, surface tillage and tillage of plowing at a different depth. Under the intensive tillage system and tillage system of plowing at a different depth the nutrients were spreading more evenly along the plow layer than under the shallow tillage. In the latter case, a higher content of nutrients was observed in the upper layers. After 20 years, the humus content in the plow layer of soil decreased significantly in all variants of the experiment. Under the prolonged usage of surface tillage the losses were by 1.5 times less than under the intensive tillage. After 40 years (1970-2011), the change of humus content in the 0-20 cm layer in comparison with the value at the experiment's beginning ranged slightly in all variants - from 0.51 to 0.57 %, while during the first 20 years (1970-1990) a more contrast discrepancy was noted - from 0.58 to 0.81 %, i.e. the deceleration of dehumification process. With the annual moldboard plowing by the end of the fourth crop rotation the humus content for the past 20 years has increased by 0.17 % and made up 3.24 %, and under disk husking decreased by 0.08 % and made up 3.26 %.