Optimized nitrogen panicle fertilizer application improves grain yield, qualities and starch traits of double-cropping early indica rice under slightly natural warming.

BACKGROUND: Early indica rice frequently encounters high temperature damage during grain-filling period in the Yangtze River basin, China induced by later sowing date, decreasing grain yield and qualities. Nitrogen panicle fertilizer application (NPF) positively mitigates the adverse effects; however, the specific details remain unclear. A field experiment using poor or high-quality early indica rice cultivars was conducted over 2 years to investigate rice yield, grain qualities and starch related traits subjected to slightly natural warming (W) under different NPF levels (Low NPF, LN; Middle NPF, MN; High NPF, HN) through delaying sowing date, with normal sowing date as the control. RESULTS: The result showed that under W, compared to LN, elevated NPF (HN and MN) significantly increased the grain yield of the rice cultivars by 11.7-21.0%, which was mainly attributed to the high effective panicle and spikelets. Elevated NPF increased the protein and amino acid contents, especially for the HN treatment, resulting in the high nutritional qualities of rice grain, at the same time as demonstrating increased hardness and stickiness, as well as decreased breakdown and amylose content, negatively affecting the eating and textural qualituies of cooking rice. Notably, compared with HN and LN, MN treatment totally enhanced the processing qualities under W in 2 years. However, HN significantly deteriorated the rice appearance qualities in the temperature treatments. These results might be a result of the unordered arrangement and irregular surface of starch granules, particular high-quality rice cultivar. CONCLUSION: The results suggest that optimizing NPF under slightly warming at grain-filling stage synergistically improve grain yield and processing qualities of early indica rice. © 2026 Society of Chemical Industry.