Effects of axial flow and tangential flow mechanical threshing on rice damage and milling quality

Abstract: Rice grains would be damaged by the mechanical threshing equipment during harvesting, and mechanical damage extent of rice grains was directly correlated to the threshing cylinder patterns and operating parameters of threshing cylinder, such as roration speed of cylinder and threshing time. On the other hand, there were not objective and whole indices to appraise the mechanical threshing damage extent of rice grains. In order to ascertain the effect of harvest pattern with different mechanical threshing cylinder on rice quality characters, taking manual harvesting rice as control group, the quality characters of the rice harvested by axial flow and tangential flow mechanical threshing cylinder were investigated. The appraisal indices of rice quality characters, fissuring rate and glume-opening rate, germination potential and rate and seedling growth properties, three-point bending breaking force, head rice yield and broken rice rate, were selected and tested according to relevant methods and standards. Experiment results show that the fissuring rate and glume-opening rate for mechanically harvesting rice are higher than that for the hand-harvested rice, and the maximum difference of glume-opening rate is about 35.6%; the fissuring rate and glume-opening rate for axial flow mechanical threshing cylinder are less than that for tangential flow mechanical threshing cylinder. But the germination potential and rate for mechanically harvested rice are lower than that for the hand-harvested rice, and the maximum difference of germination rate is 53%. The germination potential and germination rate for axial flow mechanical threshing cylinder are larger than that for tangential flow mechanical threshing cylinder, and the maximum difference of germination rate is 34%-51%. The stem length and number of roots of rice seedling for axial flow mechanical threshing cylinder and that of the hand-harvested rice are larger than that for tangential flow mechanical threshing cylinder. The maximum differences of the stem length and number of roots between tangential flow mechanical threshing cylinder harvesting and hand-harvesting are respectively 15 mm and 2.4, and those between tangential flow threshing cylinder and axial flow threshing cylinder are respectively 12.6 mm and 1.8. The stem length and number of roots of rice seedling for axial flow mechanical threshing cylinder are adjacent to that for the hand-harvested rice. There are not significant differences for root length and number of leaves and leaves length between the hand-harvested rice and mechanical threshing harvested rice. The three-point bending breaking force for mechanical harvested rice is also lower than that for the hand-harvested rice, and the maximum differences of the three-point bending breaking force for ventral side and dorsal side are 4.5 and 3.8 N respectively. There is not large difference for the three-point bending breaking force between axial flow and tangential flow mechanical threshing cylinder harvesting. The milling quality of hand-harvested rice is also superior to mechanically harvested rice, and the maximum difference of the head rice yield between them is 12.11%. The head rice yield for axial flow mechanical threshing cylinder is 10.38% higher than that for tangential flow mechanical threshing cylinder. The broken rice rate for the hand-harvested rice is correspondingly lower than that for mechanically harvested rice. Cross correlation analysis for all appraisal indices of rice quality characters manifests that the fissuring rate and glume-opening rate are cross-correlated, the germination potential, germination rate and stem length and number of roots for rice seedling are cross-correlated, the three-point bending breaking force for ventral side and dorsal side are cross-correlated, and the milled rice rate and head rice yield are cross-correlated. The mechanical threshing harvest causes the damage to rice quality, and the damage extent of rice quality for different mechanical threshing cylinder harvesting is different. The threshing damage to rice quality for axial flow threshing harvest cylinder is lower than that for tangential flow threshing harvest cylinder. Rice seeds should be harvested by using harvester with axial flow threshing cylinder. On the other hand, the appraisal indices of quality characters of rice seeds harvested by the mechanical threshing cylinder should select the fissuring rate and glume-opening rate, germination potential and rate and seedling growth properties. The appraisal indices of quality characters of food rice harvested by the mechanical threshing cylinder should be the fissuring rate and glume-opening rate, three-point bending breaking force, head rice yield and broken rice rate. The appraisal indices for the rice harvested by mechanical threshing cylinder should been wholly determined according to the used aim of rice.