Continuous Straw Returning Combined with Nitrogen Application Improve Soil Properties and Yield of Double Cropping Maize in Subtropical Regions

This study aimed to investigate the impact of straw returning (SR) combined with appropriate N application rates on soil properties and maize yield for a double cropping maize system in South China. From 2021 to 2022, a two-year field experiment was conducted (the perennial orientation study began in 2018) with two nitrogen application rates, 0 kg ha−1 (N0) and 250 kg ha−1 (N250), under various straw treatments (SR and traditional planting). The findings revealed that SR, along with the nitrogen application of 250 kg ha−1 (N250), increased soil total nitrogen (TN), soil total phosphorous (STP), and the soil total potassium (STK) content besides soil organic carbon (SOC) and labile organic carbon (LOC); similarly, their interaction improved SOC and LOC in the 0–20 cm soil layer. In addition, within the 20–40 cm soil layer, SR and N250 also increased the soil TN, SOC, LOC, STP, and STK content. Notably, these soil properties exhibited a decrease with increasing soil depth. Furthermore, SR and N250 led to improvements in the grain yield and yield component of maize. Combining SR with N250 led to a significant 101.53% increase in SOC content from 2018 to 2022. Our research indicates that implementing N rates of 250 kg ha−1 under SR is an effective method to boost maize grain yield, enhance soil chemical characteristics, and ensure safe and productive maize cultivation.