Determination of Threshing Force of Three Common Rice Varieties under Dynamic Conditions

An important biomechanical property of the rice crop for harvesting and postharvesting machines is the threshing, or requirement, force that detaches grain frompanicle. This has a principal effect on the power requirements of threshers andcombines, threshing efficiency and shattering loss. In this study, tension and pressuretesting instruments and specialized clamps were used to measure the detachmentforce. This force was analyzed in Gilan province for three common paddy ricevarieties (Hashemi, Khazar, Hybrid), three moisture content levels (12, 16, 23%w.b.), four speeds (5, 20, 35, 50 mm/min), three directions of force applied to the ricegrain (parallel to grain, perpendicular to front of grain, perpendicular to side of grain)and three panicle areas (upper, middle, lower). A randomized complete block designwas applied to analyze the data with five replications and the data means werecompared statistically. The results of the analysis of variance showed that threshingforce is significantly different in the tested varieties. The grain moisture content,direction of applied force, speed of applied force and selection location of spikelet(grain) on panicle also significantly affected the threshing force. The highest threshingforce (2.62 N) was obtained for the Hashemi variety with a grain moisture content of16% (w.b.) where the direction of applied force was parallel to the grain (tensile) at aspeed of 35 mm/min to the upper portion of the panicle.