Effects of mixed cropping Vicia sativa and nitrogen fertilizer on nitrogen yield of Avena sativa pastures in Zhaosu, Xinjiang

To evaluate the contribution of mixed planting Vicia sativa to Avena sativa grassland in reducing the use of nitrogen fertilizer and improving fertilizer efficiency, a two-factor nitrogen application levels (no nitrogen application, N₀; low nitrogen N₂₀, 20 g ·m⁻²; high nitrogen N₄₀, 40 g·m⁻² and mixed sowing ratios (grass ꞉ legume = 100 ꞉ 0, 75 ꞉ 25, 50 ꞉ 50, 25 ꞉ 75, 0 ꞉ 100) field experiment under controlled conditions was performed in the Zhaosu Basin of Xinjiang in 2019. The forage yield, nitrogen yield, and interspecific competition pattern of mixed grassland were analyzed, and the nitrogen reduction potential of mixed Vicia sativa on Avena sativa grassland was evaluated from the perspective of nitrogen yield. The results showed that: 1) Avena sativa yield, total forage yield, Avena sativa nitrogen yield, and total nitrogen yield increased significantly with an increase in nitrogen level (P < 0.05); however, the yield and nitrogen yield of Vicia sativa did not change significantly. At various levels of nitrogen application, the ratio of grass to legume 75 ꞉ 25 treatment had a higher total forage yield, and it also had a higher Avena sativa nitrogen yield under N₀ and N₂₀. The mixed sowing was advantageous, and the nitrogen application level had no significant effect on it. 2) Under N₀, the relative yield, nitrogen competition rate, and crowding rate of Vicia sativa were higher than those of Avena sativa and it were strong competitors in relative yield, nitrogen competition rate and crowding rate, while under N₂₀ and N₄₀, Avena sativa became a strong competitor. With a decrease in the mixed ratio, the relative yield, nitrogen competition rate, and crowding rate of Vicia sativa showed an increasing trend. The comparable yield, nitrogen competition rate, and crowding rate of Vicia sativa were negatively correlated with Avena sativa yield, total forage yield, and Avena sativa nitrogen yield. 3) Compared with unicast Avena sativa, mixed sowing Vicia sativa can replace 33.65%～45.15% of nitrogen fertilizer; under N₀, the contribution of mixed Vicia sativa to Avena sativa grassland was 0.45～1.28 g·m⁻²; under N₄₀, the promoted effect of mixed sowing of Avena sativa on Vicia sativa was 3.75 g·m⁻²; the increase in the yield due to applying nitrogen fertilizer was 3.71 g·m⁻². Therefore, the mixed grassland of Avena sativa and Vicia sativa in the Zhaosu area can reduce nitrogen and increase yield. The change in interspecific competition pattern has little effect on the advantages of mixed sowing and the contribution of nitrogen reduction and efficiency.