Effects of polyvinyl alcohol-chitosan binder on quality of pelleted rapeseed seeds

【Objective】This study aimed to investigate the effects of a composite binder of polyvinyl alcohol （PVA） and chitosan （CS） on the quality of pelleted rapeseed seeds， to screen the optimal PVA-CS composite formulation sui-table for climatic characteristics in southern China and requirements of mechanical precision sowing， thereby providing scientific reference for promoting and applying technologies of rapeseed pelletization in southern China.【Method】Using the main rapeseed variety cultivated in Guizhou， Qianyou 32， as experimental materials， with naked seeds （CK1） and water binder treatment （CK2） as controls， the film performance of 2% PVA， 2% CS，and their composite binders were systematically evaluated， and the effects of the composite binder on quality， germination， and seedling emergence of pe-lleted rapeseed seeds were investigated.【Result】The kinematic viscosity of binder film under CS treatment was as approximately 9 times as that under the PVA treatment； under the PC28 treatment （2% PVA and 2% CS at a volume ratio of 20∶80）， the kinematic viscosity of binder film was 21.13 mm²/s， which was significantly lower than that under the CS treatment （P<0.05，the same below）. The binder film of PC28 exhibited the optimal water absorption， with a water absorption rate of 6.93%， which was 2.13 times and 2.17 times that of the CS treatment and PVA treatment respectively. The binder film under PC28 treatment showed the best water infiltration effect， with a suitable initial contact angle and infiltration time， which was helpful for balancing water absorption and protection of seed coat for pelleted rapeseed seeds. Regarding the quality indicators of pelleted seeds， the PC28 treatment markedly improved the integrity and compressive strength of pelleted seeds compared to the CK2 treatment， as it showed balanced performance in indicators such as compressive strength （2.96 N），broken rate （0.70%），and single-seed rate （95.00%）. In terms of indoor germination， the shoot length， seedling dry weight，germination index， and vigor index of pelleted rapeseed seeds under PC28 treatment were significantly increased by 31.79%， 19.60%， 55.93%， and 72.41% respectively， compared to CK1. In terms of outdoor seedling emergence in pot， the emergence rate， seedling dry weight， and plant height were the best， increasing by 5.29%， 12.24%， and 15.80% compared to the CK1 treatment，and increasing by 18.07%， 10.37%， and 13.27% compared to the CK2 treatment.【Conclusion】The composite of PVA and CS at a volume ratio of 20∶80 serves as the optimal binder formulation for pelleted rapeseed seeds， and such composite system synergistically optimizes the mechanical strength， water absorption， air permeability，and structural stability of the pelleted coat， there by markedly enhancing the adaptability of pelleted rapeseed seeds to mechanical sowing while ensuring high seed germination quality.