Compensation of photosynthesis indexes and yield loss of wheat caused by nitrogen reduction with multiple cropping green manures

Objectives A study was conducted on the compensation effect of different green manures on the yield performance of wheat under reduced nitrogen (N) application in the Hexi Oasis irrigated area. We aimed to provide a theoretical basis for establishing green manure to replace a part of nitrogen fertilizer in wheat production.

Methods A split-plot field experiment began in 2018; cropping pattern multi-cropped mixed common vetch and hairy vetch (HCV), multi-cropped common vetch (CV), multi-cropped rapeseed (R) after wheat harvest, and no green manure (F) was the main-plot treatment. N application rate the local traditional N application 100% (180 kg/hm², N₁₈₀), 80% (N₁₄₄), and 60% (N₁₀₈) was the sub-plot treatment. We investigated the leaf area index (LAI), total leaf area duration (LAD), crop population growth rate (CGR), and net assimilation rate (NAR) during the wheat growing period (2020–2021). The yield and harvest index of wheat were measured after harvest.

Results Compared to the control (FN₁₈₀), the LAI of HCVN₁₄₄ increased by 17.7%–31.1% from the flowering to the filling stage. LAD increased by 8.4%–9.1%, CGR increased by 33.3%–133.0% from the flowering to the maturity stage, and NAR increased by 21.2%–25.1% from the flowering to grain filling stage, compared to FN₁₈₀. In 2021, the LAI of CVN₁₄₄ (except for the booting stage) increased by 10.5%–25.3% from the seedling to grain filling stage. In 2020 and 2021, LAD increased by 5.1% and 7.3%, CGR increased by 55.4%–76.7% from the flowering to maturity stage, and NAR increased by 22.5%–31.2% from the flowering to grain filling stage. At the flowering stage of RN₁₄₄, LAI increased by 7.3% in 2020, CGR increased by 22.0%–91.5% from flowering to maturity stage in 2021, LAD and NAR were not significantly different (P>0.05) in 2020 and 2021. The LAI, LAD, and CGR values from jointing to maturity stage and NAR of HCVN₁₀₈ and CVN₁₀₈ were not significantly different (P>0.05) from FN₁₈₀ for the two years. Compared to FN₁₈₀, the LAI of RN₁₀₈ was not significantly different (P>0.05) for the two years. In 2021, the LAD reduced by 4.9%, and CGR declined by 15.0% from booting to flowering. Also, the NAR decreased by 20.4% from the seedling to the jointing stage. The LAD, CGR, and NAR of RN₁₀₈ were not significantly different (P>0.05) in 2020. Compared to the control (FN₁₈₀), the grain yield of HCVN₁₄₄ (P<0.05) was improved by 13.7% and 36.1%, and the grain yield of CVN₁₄₄ (P>0.05) was improved by 9.4% and 28.4% respectively in 2020 and 2021. The grain yield of RN₁₄₄ was reduced by 5.0% compared to FN₁₈₀ in 2020, but no significant difference (P>0.05) was observed in 2021. The grain yield of HCVN₁₀₈ and CVN₁₀₈ was significantly lower than FN₁₈₀ in 2020 but not significantly (P>0.05) decreased in 2021. The 2-year grain yield of RN₁₀₈ was lower than FN₁₈₀. The harvest index of HCVN₁₄₄ and CVN₁₄₄ (P<0.05) increased by 16.9% and 14.0% compared to FN₁₈₀ in 2021, and there was no significant difference in 2020. The harvest indexes of HCVN₁₀₈ and CVN₁₀₈ were not significantly different compared to FN₁₈₀ in two years. The harvest index of RN₁₀₈ was reduced by 6.9% in 2021.

Conclusion The planting pattern of multi-cropped common vetch mixed with hairy vetch or multi-cropped common vetch after wheat harvest, increased LAI and LAD of wheat in the early and late growth stages. It also improved CGR and NAR from flowering to the grain filling stage. The loss of photosynthesis indexes in wheat caused by N reduction was compensated, stabilized, and consequently increased wheat yield. Planting rapeseed after harvesting wheat did not compensate for the grain yield loss due to N reduction.