Substituting leguminous crops for summer maize with optimal nitrogen fertilization strategies to improve soil ecosystem multifunctionality and crop production in semi-humid region

Legume crop rotation and moderate nitrogen application have been widely recognized in maintaining crop production and improving soil quality. However, the mechanism of how soybean stubble combined with appropriate nitrogen reduction regulates winter wheat growth, nitrogen uptake, and especially soil ecosystem multifunctionality (EMF), remain unclear. Therefore, a two-year field experiment was conducted using three different preceding crops (Fallow-F, Soybean-B and Maize-M) and three nitrogen application rates (N0, N1 and N2) to investigate the effects of legume pre-crops and reduced nitrogen input on winter wheat root growth, above-ground dry matter accumulation and distribution, nitrogen uptake and utilization, as well as the impact on yield and soil EMF within the cropping system. Compared with F and M stubbles, B significantly promoted the aboveground and underground growth of winter wheat, and increased nitrogen uptake by 27.48% and 33.35%, respectively. With the increase of nitrogen application rate, the root growth, aboveground dry matter accumulation and nitrogen absorption of winter wheat increased under each stubble, and the nitrogen agronomic efficiency (NAE) was significantly higher than N2 at N1 level. B stubble also significantly improved wheat yield, annual economic benefits and EMF, with the best performance observed at N1, where the economic benefits of BN1 were on average 70.87% higher, and EMF was 4.17 times higher than other treatments. Pearson correlation analysis revealed positive relationships between winter wheat root dry weight (RWD), above-ground biomass and grain nitrogen accumulation, as well as a positive correlation between EMF and wheat yield. These findings highlight the close relationship between winter wheat root and above-ground growth and nitrogen uptake, while also revealing the importance of soil EMF in wheat yield. This study provides theoretical support for incorporating legumes into cropping systems to reduce chemical nitrogen fertilizer use and enhance soil ecosystem multifunctionality.