Compensation of green manure on photosynthetic source and yield loss of wheat caused by reduced irrigation in Hexi oasis irrigation area

Objectives Water shortage severely restricts wheat production in Hexi oasis irrigation area. Growing and returning green manure after wheat harvest has been proved to be an effective way of improving wheat yield. We investigated the compensation effect of green manure on wheat growth under condition of irrigation reduction.

Methods A field experiment of multiple cropping green manure after wheat harvest was established in Hexi Oasis irrigation area in 2017, with wheat cultivar Ningchun 4 and Vicia sativacultivar Lanjian 2 as tested materials. Three irrigation levels (i.e., traditional irrigation (540 mm, I₃), reduced irrigation by 50 mm (490 mm, I₂), and reduced irrigation by 100 mm (440 mm, I₁) were setup, and under each irrigation level, three green manure treatments after wheat i.e., planting and returning green manure to farmland (WG), planting but not returning green manure to farmland (WGr), and kept fallow (WF) were setup. The photosynthetic leaf area index (LAI), leaf area duration (LAD) and yield of wheat were investigated in 2019–2021.

Results During the whole growth periods, compared with I₃ in 2020 and 2021, I₁ decreased wheat LAI by 6.26% and 5.84%, and LAD by 6.21% and 5.87%, I₂ decreased LAI by 3.55% and 2.85%, and LAD by 3.17% and 3.13% (P<0.05), respectively. Compared with WFI₃, WGI₂ increased wheat LAI and LAD by 2.31% and 3.07% respectively in 2020, and by 3.69% and 4.03% respectively in 2021. However, WGrI₂ had similar LAI and LAD values, indicating the significant compensation of green manure incorporation. Compared with I₃, I₁ decreased dry matter accumulation (DMA) and grain yield (GY) by 16.31% and 14.00% respectively in 2020, and by 15.19% and 12.98% respectively in 2021; I₂ decreased DMA and GY by 6.20% and 1.78% respectively in 2020, and by 6.58% and 4.05% respectively in 2021. Compared with WFI₃, WGI₂ increased DMA by 4.84% and 5.30%, GY by 5.89% and 6.01%, while WGrI₂ had similar DMA and GY, indicating the compensation effect of green manure incorporation. The compensation effect of planting green manure on the photosynthetic source and dry matter accumulation under I₂ in 2021 was better than that in 2020. WG compensation on yield was mainly attributed to the simultaneous compensation of wheat LAI and LAD.

Conclusions In Hexi Oasis irrigation area, planting and incorporating green manure could achieve similar photosynthetic source and yield of wheat in the following year. Overall, compensation for the loss of photosynthetic source and yield of wheat caused by reducing 50 mm of conventional irrigation amount, therefore, it is a practical water saving technology for wheat production.