Effects of sowing date and density on lodging resistance and yield of different rapeseed cultivars

To study the effects of late sowing and density on the lodging resistance and yield of rapeseed, and to provide the theoretical and technical support for the mechanized production of rapeseed, using three canola varieties（Shaanyou 28, Qinyou 28, and Qinyou 7） as the experimental materials, three sowing dates（T1: September 24, T2: October 1, and T3: October 8）, and three densities(D1: 225,000 plants hm , D2: 450,000 plants hm , and D3: 675,000 plants hm ) were set up to analyze the yield and constituent factors, the indexes related to lodging, the main components of the stem and the microstructure of the stem. The results showed that:（1） Under T1 and T2 treatments, with the increase of plant density, the yield of each plant of the three varieties decreased, the group yield increased first and then decreased, the lodging index decreased first and then increased, the vascular bundle and stem cross-sectional area decreased, the vascular bundle area/stem cross-sectional area, stem lignin, and cellulose content inc