Influence of nitrogen fertilizers on protein productivity of vetch-wheat grain under different water supply conditions

The peculiarity of nitrogen nutrition for legume-cereal mixtures is that due to the intravital transfer of mineral nutrition elements from the legume component of the mixture to the cereal component and vice versa, the cereal component receives nitrogen from the air symbiotically fixed by the legume component. This explains its better development in the mixture than in single-species sowing without the use of nitrogen fertilizers. In unfavorable conditions for legume-rhizobial symbiosis, when the assimilation of air nitrogen is weakened, and the legume and cereal components of the mixture are deficient in nitrogen, therefore, the issue of nitrogen fertilizer use expediency for legume-cereal mixtures is relevant. We have studied the effects of low and medium doses of nitrogen fertilizers including 30, 60 and 90 kg ha^-1 (as treatments N₃₀, N₆₀ and N₉₀) on the content and yield of crude protein with the grain yield of the vetch-wheat mixture under the conditions of sod-podzolic sandy loam soil in the central region of the Non-Chernozem zone with insufficient and optimal moisture. The protein content (% of dry matter) was determined by the calculation method according to the nitrogen content (N% × 6.25). On the control without nitrogen fertilizers, the protein content in vetch seeds and in wheat grain under the conditions of optimal moisture (2019) was higher than under the conditions of insufficient moisture (2018), by 0.4% and 0.3%, respectively. Nitrogen fertilizers increased the protein content in wheat grain by 0.2 - 0.4% during both years of study. The protein content in vetch seeds under the influence of nitrogen fertilizers increased only under the conditions of insufficient moisture by 0.2-0.7%. The protein yield with the wheat grain yield during both years of study upraised, as the dose of nitrogen fertilizers elevated by 1.6 - 2.7 times, and by the vetch harvest and insufficient moisture it remained unchanged, and by optimal moisture it droped by 13.7-34.7%. The protein yield with the grain yield of the mixture elevated by 44.4-91.1% under the influence of nitrogen fertilizers in arid conditions completely due to the wheat protein increase, while in conditions of sufficient moisture it droped by 5.2-17.8% due to the vetch protein decrease. Nitrogen fertilizers increased the competitiveness of wheat mixed with vetch under the conditions of insufficient moisture by 1.7-3.0 times, and under the conditions of optimal moisture by 1.9-4.1 times.