Harvesting and threshing methods for Paddy-II: A Review

Threshing of paddy crop is carried out using manual, animal or mechanized power sources depends on the farmland size. In a thresher, rasp bar, spike tooth, peg tooth and wire-loop type threshing elements can be fitted with the threshing cylinder irrespective of direction of crop feed and flow. Different elements are responsible to thresh the crop with different actions which include impact, rubbing, combing, squeezing and their combination. This review was carried out to explore the effect of different threshing elements and threshing methods on performance of paddy threshing. Unlike threshing of other cereal crops, hull removal is not required in paddy. Selection of threshing elements based on the crop to be threshed. The type of threshing element determines the threshing efficiency, energy requirement and grain loss. Among rasp bar, spike tooth, peg tooth and wire-loop type threshing elements, wire-loop type was found to be most suitable for paddy threshing. Factors like cylinder speed, cylinder type and diameter, concave clearance and throughput rate affect the threshing performance. A low speed of cylinder produces more un-threshed grains. It can be compensated using for axial flow thresher as it has high crop retention period. Contrarily, a high speed is responsible for better threshing efficiency along with the more grain breakage and energy consumption. Using tangential flow thresher crop retention period can be minimized. The work rate of pedal and power thresher was, respectively 2 and 10 times more than that of manual threshing. The average threshing efficiency of pedal thresher, power thresher and combine harvester was reported to be 97 to 99%, 96.30 to 99.75% and 98.5%, respectively.