Abstract: Lodging is one of the important constraints to high yield and stable production of rice. This study investigated the effects of nitrogen and cultivation density application on stem lodging resistance and its relationship with stem morphological and mechanical traits. The mechanisms of stem lodging resistance were explored. Results of the study would provide a theoretical basis for lodging resistance and high yield cultivation of rice. Three indica rice cv. hybrid late rice varieties with different lodging resistance were grown in field experiments conducted with three nitrogen and three cultivation density levels at Shangrao. Lodging index, morphological and mechanical traits of basal culms were measured. Results showed that with the increase of nitrogen fertilizer and plant density, the first stem basal internode became spindling, the second and third internode length showed increasing first and then fall, stem wall became thinning, stem type index decreased, which improved the ability of stem lodging index and reduced lodging resistance; The rice group was large under the cultivation of high nitrogen and density, which inhibited it's growth, and increased angle of inclination and lodging index of rice stem leading to easy lodging. The lodging index had positive correlation with plant height, basal elongation internode length and negative correlation with stem diameter, stem thickness, type index; To a certain extent, increasing nitrogen fertilizer and density could increase the stem length and bending moment, reduce the wall thickness, mechanical strength, and bending moment (M), which reduced the lodging resistance capability, improved rice stem lodging index (LI). Lodging resistance of rice were stronger under medium nitrogen fertilizer (160 kg·hm^-2) and density (20.0 cm×16.6 cm) cultivation condition.

Key words: hybrid late rice, cultivation condition, lodging resistance, stalk physical characteristics, mechanical property