Co-Ridge Planting Enhances Yield Advantages of Maize Intercropping with Peanut by Improving Soil Aggregate Stability and the Ecological Stoichiometric Characteristics of Carbon, Nitrogen, and Phosphorus

Long-term maize (Zea mays L.) intercropping with peanut (Arachis hypogaea L.) (M||P) improves soil aggregate stability and phosphorus (P) availability, sustaining farmland productivity. In contrast, co-ridge planting (R-M||P) further enhances yield. However, the relationship between yield increase and improvements in soil aggregate stability and ecological stoichiometric characteristics under R-M||P remains unclear. Therefore, this study examined the effects of R-M||P on aggregate fractions and stability, bulk density (BD), porosity (Pt), soil organic carbon (SOC), total nitrogen (TN), available phosphorus (AP), total phosphorus (TP), and inorganic phosphorus, along with the ecological stoichiometric characteristics of C, N, and P. R-M||P substantially increased the proportion of topsoil macroaggregates, both mechanically stable (>0.5 mm) and water-stable (>1 mm), compared with flat planting. Additionally, it enhanced WR0.25 and mean weight diameter, substantially reduced BD, and increased Pt. Furthermore, R-M||P significantly increased the concentrations of SOC, TN, TP, AP, Ca2-P, Ca8-P, Al-P, and Fe-P. It also enhanced the contribution rates of SOC, TN, TP, and AP in macroaggregates, leading to increased storage of carbon (SCS), nitrogen (SNS), and phosphorus (SPS). R-M||P significantly elevated C:N and C:P ratios. Phosphorus application increased SOC and nutrient concentrations, positively regulated C:N, and enhanced C, N, and P storage. However, it negatively influenced C:P and N:P ratios. SOC and AP were the main driving factors affecting the intercropping advantage, with explanatory rates of 33.2% and 22.7%, respectively, under R-M||P. These findings suggest that R-M||P combined with P application enhances yield by promoting aggregate stability, increasing the concentrations and storage of C, N, and P, and establishing a new ecological stoichiometric balance.