Aiming at the problems of large nitrogen input, single fertilizer source, low nitrogen utilization rate, and poor quality of wheat in spring wheat cultivation in Hexi areas of Gansu Province, the objective of this study is to explore the effects of suitable green manure and reduced nitrogen fertilizer cultivation techniques on grain yield and quality, and nitrogen absorption and utilization of spring wheat, and to provide a theoretical basis for high yield, high quality, and green production of wheat in Hexi irrigation areas.

A split plot experiment was conducted from 2019 to 2021 in the Hexi oasis irrigation areas of Gansu Province. Two cropping patterns of multiple green manure after wheat (W-G) and sole wheat (W) were set in the main plot. There were five N fertilizer levels in the sub-plot: 100% of conventional N fertilizer by the farmer (180 kg·hm^-2, N₄), 85% of conventional N fertilizer (N₃), 70% of conventional N fertilizer (N₂), 55% of conventional N fertilizer (N₁), and no N fertilizer (N₀).

Multiple green manure after wheat combined with 85% N application (W-G-N₃) was effectively increased wheat grain yield and biomass. The grain yield of W-G-N₃ was increased by 16.7%-18.4% and 13.6%-34.4%, respectively, compared with the 85% N application (W-N₃) and conventional N application (W-N₄) treatments for the sole wheat. The biomass of W-G-N₃ was increased by 11.3% (2020) and 5.2%-11.6% (2020 to 2021), respectively, compared with the W-N₃ and W-N₄ treatments. The increase of grain yield was greater than that of biomass, thus, the W-G-N₃ treatment had higher harvest index, which was 4.9%-15.9% and 8.0%-20.5% higher than that of W-N₃ and W-N₄ treatments. Meanwhile, the W-G-N₃ treatment improved grain quality of wheat by increasing protein content, sedimentation value, and wet gluten content, among which, the protein content, sedimentation value, and wet gluten content of W-G-N₃ were increased by 12.3%-16.1%, 28.7%-47.2%, and 10.7%-11.1%, respectively, compared with W-N₃; The protein content of W-G-N₃ was increased by 8.9%-12.4% compared with W-N₄, but the differences in sedimentation value and wet gluten content between W-G-N₃ and W-N₄ were not significant. In addition, the W-G-N₃ treatment was beneficial to promote nitrogen uptake and conversion to grain yield in wheat compared with W-N₃ and W-N₄ treatments, in which the N uptake was increased by 42.2%-58.9% and 35.2%-45.0%, N use efficiency was increased by 12.0%-20.6% and 5.9%-20.4%, respectively, and N partial factor productivity was increased by 3.6%-18.3% and 28.1%-58.1%, respectively. The W-G-N₃ treatment could compensate for the reduction of N agronomic efficiency, which was 74.2%-80.0% higher than W-G-N₄ treatment. The correlation analysis showed that multiple green manure after wheat combined with moderate reduction of N fertilizer increased grain yield by promoting efficient nitrogen uptake and utilization, and also significantly improved grain nutritional quality.

The combination of multiple green manure after wheat with 85% (153 kg·hm^-2) nitrogen application is the suitable cropping pattern and nitrogen application level to boost wheat yield, improve wheat grain quality, and increase nitrogen use efficiency in Hexi oasis irrigated areas.