Grain yield and water productivity of winter wheat controlled by irrigation regime and manure substitution in the North China Plain

Manure application is considered a good way to modify soil structure and hydraulic properties and has the potential to promote water productivity. Therefore, the potential for improving water savings and water productivity through the use of manure as a substitute for mineral fertilizer is worth further exploration in deficit irrigation regions. A field experiment with four irrigation regimes and four types of fertilizer inputs was conducted in the North China Plain. The irrigation regimes included W0 (no irrigation), W1 (irrigation at the presowing stage only), W2 (irrigation at the presowing and jointing stages), and W3 (irrigation at the presowing, jointing, and anthesis stages). The fertilizer inputs included CK (no fertilizer), M0 (mineral fertilizer only), M50 (half mineral plus half manure), and M100 (manure only). Sixteen treatments were laid out in 2012, and samples were collected in 2018–2019 and 2019–2020 during the winter wheat growing season. The results showed that the greatest potential to improve water productivity and obtain a greater grain yield occurred in W2 than in W3 while interacting with precipitation; both of these grain yields were significantly greater than those in the other irrigation treatments. The leaf area index (LAI) plays an important role in regulating soil water consumption and is negatively correlated with evaporation accumulation and the ratio of evaporation to evapotranspiration. However, compared with those under pure mineral fertilizer application, the LAI under manure application alone could not ensure an equal LAI, and the grain yields under M100 were significantly lower than those under M0 by 7.66% and 13.62%, respectively, during the two years. In addition, no advantage in water productivity was observed in M100. However, half-manure substitution for mineral fertilizer maintains a reasonable LAI and grain yield, and its combination with W2 benefits the improvement of water productivity. The study showed that total manure substitution for mineral fertilizer has limitations in improving water productivity, but partial manure substitution combined with irrigation at the presowing and jointing stages has great potential in maintaining high grain yield and improving water productivity. The results of this study could lead to further research exploring the potential for improving water productivity by applying organic fertilizer in the North China Plain.