Potential of nitrogen reduction for maintaining wheat grain yield under multiple cropping with leguminous green manure in irrigated oasis

Objectives We studied the potential of N reduction on yield and yield components of wheat under multiple cropping with leguminous green manure. This study aims to provide a scientific and practical basis for efficient wheat production when green manure replaces chemical N fertilizer in irrigated oasis.

Methods A split plot design field experiment was conducted at Wuwei, Gansu Province, China, in 2018–2019. Cropping pattern i.e., planting hairy vetch (Vicia villosa Roth, HV) after wheat harvest (W-G) or planting of sole wheat (W) was the main plot/factor, while N application rate i.e., 45% (N₁), 30% (N₂), 15% (N₃), 0 (N₄) reduction of the conventional N input (180 kg/hm²), and no N input (Control, N₀) was the sub-factor. Dry matter accumulation during the whole growth period, grain yield, and yield components were measured. A successive interpolation method was adopted to quantify the potential of N reduction.

Results Compared with W treatments, W-G increased grain yield by 10.8% in average. The wheat yield in W-G-N₃ was similar to that in W-G-N₄, but was 6.9% and 7.9% higher than those in W-N₃ and W-N₄, respectively. The harvest index in W-G-N₃ was 27.2% and 16.7% higher than those in W-N₃ and W-N₄, respectively. The N replacement potential in W-G-N₃ treatment was 27.5% and 39.0% higher than that in W-G-N₂ and W-G-N₁, respectively. The maximum growth rate of wheat in W-G-N₃ treatment was 6.0%, 28.4%, and 23.8% higher than those in W-G-N₄, W-N₃, and W-N₄, respectively. The W-G-N₃ treatment increased spike number per area, kernel number per spike, and thousand-kernel weight. According to the grey correlation analysis, the correlations of thousand-kernel weight, maximum growth rate, kernel number per spike, and spike number with wheat yield were in descending order.

Conclusions The maximum growth rate, highest thousand-kernel weight, and relatively high yield and harvest index of wheat were obtained under 15% reduction in conventional N application rate. Therefore, 15% reduction in conventional nitrogen application rate in a multiple cropping system is suitable for optimal wheat production in irrigated oasis of Gansu Province.