Elevated Nitrogen Fertilization Compromises Lodging Resistance in High-Quality, Late-Season Indica Rice Grown in Southern China

While nitrogen is essential for rice production, excessive application promotes lodging, threatening yield stability. In this study, we evaluated the impact of three nitrogen application rates (105, 165, and 225 kg ha−1) on yield formation and lodging resistance in two elite late-season indica rice varieties—Meixiangzhan 2 (MXZ2) and Taiyou 871 (TY871). Our findings demonstrate that (1) elevated nitrogen increased productive panicle number but reduced grains per panicle and percentage of filled grains. (2) High nitrogen inputs substantially elevated the lodging risk, with the lodging index increasing by 20.4% and 45.7% in MXZ2, and by 15.4% and 38.3% in TY871, at 165 and 225 kg ha−1, respectively. (3) Reduced mechanical strength—associated with impaired morphological structure (e.g., increased plant height and height of gravity center), diminished structural carbohydrate content in sheaths and culms, and expanded pith cavity area—collectively contributed to the increased lodging susceptibility with elevated nitrogen. (4) MXZ2, though lower-yielding, exhibited greater lodging resistance than TY871, owing to its superior culm anatomy and sheath strength. (5) Interannual climate variation—particularly low temperature and light intensity in 2020—amplified the negative effects of high nitrogen. Our results provide insights into nitrogen-driven trade-offs between yield and lodging, supporting tailored nitrogen management strategies for indica rice under varying environmental conditions.