Nitrogen Flows in Agrocenosis of Winter Wheat Under Conditions of Different Reactions of Typical Chernozem Medium (Based on Application of 15N)

It is shown that an increase in winter wheat on typical chernozem characterized by the acid reaction of the soil medium leads to a decrease in grain yield to 30% and straw weight to 25%. The crop reached the maximum level after introducing urea and manure wastes (the yield gain was 199% in neutral soil and 165% in acidic soil). The improvement of plant nitrogen nutrition by introducing fertilizers led to an increase in the protein content in grain by 1.2 times on both soils; at the same time, the protein content was 1.1 times lower in acidic soil than in the neutral one. The maximum content of protein in winter wheat grain accumulated after both types of fertilizers were applied on neutral soil; the use of manure wastes alone decreased the protein content in grain. It has been revealed that a decrease in the yield of grain and a decrease in the content of crude protein in this grain after acidification of typical chernozem is due to a decrease in the amount of mineral nitrogen in soil and an increase in its gaseous losses. The pattern of nitrogen transformation in soil, as well as the availability of nitrogen for the plants, varied as the reaction of the medium changed. In acidic soil, the consumption of mineral fertilizer nitrogen and manure wastes by the plants decreased by 12–13% and the consumption of soil nitrogen decreased by 45%. The effect of wastes decreased the consumption of urea nitrogen by 49% (neutral soil) and by 69% (acidic soil). The consumption of fertilizer nitrogen by the plants decreased by 12–15% after acidifying typical chernozem and by 12–17% after immobilizing this type of chernozem and increased gaseous losses by 18–81%. It has been concluded that the agrophytocenosis of winter wheat maintains the ecological balance (homeostasis) when wastes from a pig-breeding complex are used and is exposed to stress when urea is applied in acid chernozem. Soil acidification decreased the resistance of agrophytocenosis to the level that is observed when manure wastes were applied and to adaptive depletion when urea was used.