Partial substitution of chemical fertilizer by green manure increases succeeding maize yield and annual economic benefit in low-yield cropland in the Yellow River Delta

Green manures (GM) combined with fertilizer reduction is an efficient measure to alleviate the environmental issues caused by the overapplication of chemical fertilizer. However, both the environmental and economic benefits remain unclear in coastal regions that are affected by both soil salinization and climate change. A field experiment was conducted in low-yield cropland in the Yellow River Delta to explore the effects of green manure rotation combined with fertilizer reduction on the soil environment and economic sustainability. Two GM species, Vicia villosa (HV) and Orychophragmus violaceus (OV), a traditional winter wheat (Wheat), were grown in winter, with a fallow control (Fallow). In the subsequent maize season, three fertilizer rate treatments, a full rate of 600 kg ha⁻¹ compound fertilizer (F100), 85% of the full rate (F85), and 70% of the full rate (F70), were applied in each former treatment. The results indicated that GM return markedly increased soil total N (TN) and P (TP) before the V6 stage of maize (when maize had 6 leaves). The average TN contents of HV and OV increased by 56.9% and 38.5%, respectively, compared with that of Wheat, while the values for TP were 13.6% and 16.9%. Compared with Fallow, the maize yields of HV and OV increased by 25.6% and 13.8%, respectively, while that of Wheat decreased by 9.1%. The average partial fertilizer productivities (PFPs) for HV and OV increased by 25.3% and 14.0% compared with Fallow, while Wheat decreased by 8.9%. The PFPs for F85 and F70 increased by 19.4% and 37.7%, respectively, compared with F100. Reducing the fertilizer rate to 70% in the HV–maize rotation pattern did not reduce but increased the total net profit and rate of return. Thus, HV–maize rotation combined with 30% fertilizer reduction is suggested for sustainable agriculture in this region.