Nitrogen application and soil mulching improve grain yield of rainfed maize by optimizing source-sink relationship and grain filling process on the Loess Plateau of China

The kernel weight of maize (Zea mays L.) is largely regulated by the source-sink relationship during the grain-filling period. The source-sink coordination is the key to high grain yield, which is affected by many management practices, such as nitrogen application and soil mulching. Previous studies have mainly focused on qualitative descriptions of maize source-sink relationships, but the quantitative analysis of maize source-sink relationships under various nitrogen application rates and soil mulching practices have been poorly explored. A three-season (2020–2022) experiment was conducted on rainfed maize on the Loess Plateau of China, with two nitrogen rates (N, 0 kg N ha; N, 180 kg N ha) and three mulching practices (NM, flat cultivation with no mulching; SM, flat cultivation with full straw mulching; RF, ridge-furrow cultivation with transparent film mulching on the ridge). The results showed that compared with N, N increased the maximum leaf area index (LAI) by 29.6%, leaf area duration (LAD) by 31.4%, maximum 100-kernel weight (HGW) by 12.5%, source growth (SG) by 34.2%, sink capacity (SC) by 49.8%, source supply rate (SUR) by 23.4%, sink growth rate (SGR) by 50.7%, and finally increased grain yield by 37.2%. Compared with NM, SM and RF increased LAI by 8.5% and 25.6%, LAD by 10.6% and 28.0%, HGW by 5.5% and 10.3%, SG by 13.6% and 41.6%, SC by 16.4% and by 35.5%, SUR by 8.7% and 35.5%, SGR by 16.3% and 37.1%, and finally increased grain yield by 8.2% and 26.7%, respectively. The structural equation modeling indicated that LAD mainly affected SG, and SG significantly affected source-sink relationships and grain-filling parameters, which mainly affected 100-kernel weight and the number of grains per spike, respectively. The number of grains per spike had a greater impact on the sink capacity than 100-kernel weight. In conclusion, nitrogen application and soil mulching enhanced grain yield of rainfed maize by increasing leaf source size, promoting source growth and grain filling, improving kernel number and optimizing source-sink relationships on the Loess Plateau of China. This study provides a better understanding of source-sink relationships for optimizing maize management practices and identifying key processes in modeling maize yield.