Effects of threshing and post-threshing recovery methods on postharvest losses in two varieties of rice

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Rice is the most important cereal crop for human consumption. Over three (3) billion people are depending on rice as a staple food. The consumption of rice in Africa is far more than its production level on the continent, several hundred million people are depending on rice cultivation and post-harvest activities as their main source of employment particularly in the rural areas. In the developing countries, significant volumes of grain are lost after harvest, aggravating hunger and resulting in expensive inputs-such as fertilizer, irrigation water, and human labor-being wasted and therefore postharvest system for rice deserves special attention, where the implementation of postharvest technologies is urgent in order to prevent food rice losses. The main objective of the research was to determined the influence of various processing methods on postharvest losses in two varieties of rice at Nobewam lowland irrigated rice field in the Ashanti Region of Ghana. The design of the experiment was 2 x 3 x 3 factorial arrangement in randomized complete block design with three replications. The factors were variety at two levels : Jasmine 85 and Sikamo; threshing methods at three levels: Bambam, Drum, Sack and post-threshing recoveries at three levels Pounding, Pounding plus hand-picking and straight had-picking. The result indicated that, Jasmine 85 recorded the highest threshing losses from the various threshing methods and recoveries employed. Sikamo recorded the least losses. Between the threshing methods + recoveries employed, the Drum-based methods, resulted in the highest losses whereas the least losses were obtained from the Sack-based methods. Threshing of Sikamo using vii the sack method took the longest time to complete threshing significantly longer than the time by the other treatment combinations. The shortest threshing time was produced by threshing Sikamo using the bambam method though not significantly different from the time spent to thresh Jasmine 85 using either bambam or drum method. Threshing Sikamo using the sack method used 2.9 times more time than threshing Sikamo using the bambam method. Among the varieties, the time spent on threshing Jasmine 85 was 32 % significantly less than that spent on threshing Sikamo. In terms of the threshing methods, using the bambam took significantly less time than either the drum or sack, the differences being 32.4 % and 58.4%, respectively. In addition, for the post-threshing recoveries, large quantity of grains were recovered from pounding + hand-picking of Sikamo and small quantity was resulted from the straight hand-picking of Jasmine while the methods, the Drum recorded the highest recovery of grains and the lowest was from the Sack. The greatest economic benefit was accrued from the Sikamo - sack + recoveries technology. The Jasmine - bambam + recoveries technology resulted in the least economic benefit. Between the methods, there was a 13.8 % increased benefit from using the Sack-based methods as compared to the Bambam-based methods. Similarly, there was a 7.3 % increased benefit from using the Sack-based methods as compared to the Drum-based methods. Comparing the Drum-based and Bambam-based methods, there was a 6 % increased benefit of using the Drum-based methods. Among the varieties, there was no economic advantage of using one variety over the other.
A thesis submitted to the School of Research and Graduate Studies, Kwame Nkrumah University of Science and Technology, in partial fulfillment of the requirements for the award of Master of Philosophy degree in Postharvest Technology.