Differential improvement in soil quality and maize productivity between individual and mixed green manures

Green manuring in agroecosystems is an efficient fertilization management method for improving soil properties and crop productivity. However, most studies have focused on the implications of individual green manure, and little attention has been paid to mixed cropping green manure. Therefore, we examined the impacts of the individual and mixed cropping of green manure on soil quality, soil properties, and crop productivity in the Northern China Plain. The results showed that hairy vetch (HV) with or without other green manures have significant enhancement in soil quality index (SQI) values. Specifically, the SQI values increased by 0.14–0.34 relative to other green manure treatments. Mixed cropping (HV with Orychophragmus violaceus ) (HV+OV) and (HV with rye) (HV+R) contributed to increases in SOC, AN, AP, AK, DOC, MBC, MBN, and fine-clay contents, while HV contributed to TN, TP, and TK increases, as well as decreases in soil pH, compared to the levels observed when using other green manures. The application of green manure (except HV) significantly increased the dissolved organic matter (DOM) quantity compared to that of winter fallow (F), with mixed cropping showing particular superiority. Among all green manures, OV significantly enhanced DOM aromaticity, hydrophobicity, and humification. Both individual and mixed green manures had distinct effects on the maize yield and grain nutrient accumulation. Notably, mixed green manures, particularly HV + OV, significantly increased maize yield compared to that of F. Moreover, HV maize grains exhibited the highest nitrogen accumulation, and a Mantel test suggested that the increase in maize yield and grain nutrient accumulation was mainly due to improvements in soil properties and the SQI. The crop productivity was found to exhibit a stronger correlation with the quantity of DOM compared to its structural characteristic Our results indicated that individual or mixed green manuring was differentially associated with maize yield and grain nutrient accumulation by enhancing the soil quality, soil properties, and optical properties of soil DOM in the Northern China Plain.