Optimization of straw incorporation and nitrogen fertilizer affects maize starch synthesis and grain yield in Northeast China

Straw incorporation combined with suitable nitrogen (N) fertilizer is considered a key strategy for improving soil health, optimizing resource use efficiency, and thus developing environmentally friendly agricultural systems. However, the effects of straw incorporation practices and N fertilizer rates on the complex relationships between crop starch synthesis and yield are not fully understood. We investigated the effects of two straw incorporation practices and four N fertilizer levels on the key physiological parameters of grain filling and yield during 2023–2024. Compared to rotary tillage combined with straw incorporation (RTS), plow tillage combined with straw incorporation (PTS) significantly increased leaf photosynthetic metabolism and grain sugar accumulation by enhancing enzyme activity, contributing to higher starch accumulation, plant biomass, and grain yield over the two years of study. The treatment using 187 kg N per ha -1 (N2) resulted in a higher leaf photosynthetic capacity and grain sugar contents compared with the other N fertilizer treatments. The stimulative physiological features were conducive to regulating the grain-filling process and providing a higher filling rate and longer filling period in the PTS treatment combined with N2 practices. In contrast, RTS combined with a low N content was beneficial for optimizing the pasting quality of starch. Overall, our results establish a physiologically grounded framework for reconciling yield and nutritional enrichment, offering actionable strategies for transforming maize production demands through straw incorporation and N fertilizer stewardship. • Straw and N fertilizer affected photosynthetic metabolism and sugar accumulation • High N reduced enzyme activities for starch synthesis in both straw incorporations • PTS combined with 187 kg N ha -1 significantly improved maize grain yield • RTS provided superior starch pasting properties to PTS