Biomechanical properties of ready-to-harvest rapeseed plants: Measurement and analysis

A large loss occurs in the combine harvesting of rapeseeds due to the fragility of rapeseed pods, and all the more so with the vibration of the combine header and the collision between the header and plants. Seed loss is greatly affected by the biomechanical properties of ready-to-harvest rapeseed plants. To understand the mechanism of pod cracking and seed loss and to propose measures for alleviating them, it is needed to study the biomechanical properties of ready-to-harvest rapeseed plants. To this end, “Huayouza 62”, a widely planted rapeseed variety in central China, was selected to study the biomechanical properties, including pod-cracking resistance, main stem-shearing resistance and resonant frequencies, of whole plants. The results showed that the distribution of pod-cracking resistance forces was 1.333–6.100 N in the mature stage, and the pod width and thickness had a significant influence on the cracking resistance. The main influencing factor of the main stem-shearing resistance was the stem diameter. A thicker main stem resulted in a larger shearing resistance force but a smaller shear stress. The moisture contents of the main stems varied from 47.71% to 76.13%. However, the varying moisture contents did not show a significant impact on the shearing resistance. The resonant frequencies of whole rapeseed plants ready for harvest ranged from 6.5 Hz to 7.5 Hz, which was close to the excitation frequency of the cutter bar on the 4LL-1.5Y harvester. This study lays a foundation for improving the design and construction of harvesting devices for rapeseed plants to reduce seed loss.