Transactions of the ASAE Vol. 47(3): 599-605 E 2004 American Society of Agricultural Engineers ISSN 0001-2351 599 SOYBEAN THRESHING MECHANISM DEVELOPMENT AND TESTING S. Fernando, M. Hanna, C. Mesquita ABSTRACT. Soybean harvesting is done predominantly with combine harvesters. The size, sophistication, and operational costs of this modern machine make the combine harvester unaffordable for the small-scale farmer, especially in developing countries. Research has shown that the energy required to process the whole plant in the conventional combine is much greater than that required to open the soybean pods. An alternative soybean harvester was developed to thresh soybeans while the soybean plants were still rooted in the ground. The unit, which employed rotating plastic cords to impact and open the seed pods, was field tested with shaft rotational speeds of 1000, 1800, and 2600 rpm at different times of the day. The threshing efficiencies of the threshing mechanism, operating at 1000, 1800, and 2600 rpm, were <50%, 87.3%, and 93.7%, respectively. Seed breakages of 0.35% to 1.11% and seed coat damages of 11.8% to 16.6% were observed. The energy required to thresh one hectare of soybeans was estimated to be 6 to 9 MJ, excluding the power required to propel the equipment. Keywords. Soybean harvesting, Soybean harvesting losses, Soybean seed quality, Soybean threshing. ombine harvesters are used almost universally for harvesting soybeans. The improvements inherent in harvester designs have contributed generally to an increase in their size, price, and operating costs, making them unaffordable for the average farmer in the world (Mesquita, 1989). Mesquita and Hanna (1995) found that the amount of energy required to open soybean pods was considerably lower than the energy utilized to process the whole plant. Quick (1972) and Mesquita and Hanna (1995) discovered that material other than grain (MOG) corresponded to 60% of the total volume of plant material processed during conventional combine harvesting. These findings led Mes- quita et al. (2000) to develop an alternative soybean harvesting and threshing unit that threshed the soybean pods while the plant was still rooted in the ground, thus eliminating cumbersome processing steps in the conventional combine harvesting method. A prototype harvester was initially developed at the National Center for Soybean Research of Embrapa (Brazilian Agricultural Research Corporation), Londrina, Parana State, Brazil, and preliminary field tests were done there. An independent study was carried out by the Department of Biological Systems Engineering, University Article was submitted for review in August 2002; approved for publication by the Power & Machinery Division of ASAE in March 2004. Presented at the 2002 ASAE Annual Meeting as Paper No. 02-1061. The authors are Sandun Fernando, ASAE Member, Assistant Professor, Department of Agricultural and Biological Engineering, Mississippi State University, Mississippi State, Mississippi; Milford A. Hanna, ASAE Member, Professor, Department of Agricultural and Biological Systems Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska; and Cezar Mesquita, Visiting Faculty, Industrial Agricultural Products Center, University of Nebraska-Lincoln, Lincoln, Nebraska. Corresponding author: Dr. Milford A. Hanna, 208 L. W. Chase Hall, Department of Agricultural and Biological Systems Engineering, University of Nebraska-Lincoln, Lincoln, NE 68583-0730; phone: 402-472-1634; fax: 602-472-6338; e-mail: mhanna1@unl.edu. of Nebraska-Lincoln, to further develop the concept and improve the prototype. OBJECTIVES This study was conducted to: S Perform field trials and evaluate threshing efficiencies of the alternative soybean threshing mechanism in order to determine optimum operating conditions. S Evaluate threshed seed quality in terms of seed breakage and seed coat damage. S Evaluate the power requirement of the threshing device. REVIEW OF LITERATURE According to Mesquita (1989), the dehiscence character- istic of soybean pods directed most of the initial research on soybean harvesting, leading to improvements in combine header components to reduce seed losses from pod shatter- ing. One major area on which researchers have focused is the redesign of the cutterbar. In the process of soybean harvesting, threshing undoubt- edly is the most critical operation because the seed is subjected directly to externally applied mechanical forces. In order to reduce impact damage, while achieving the maxi- mum threshing efficiency, various mechanisms have been incorporated into harvesting machinery. Although the mechanisms for accomplishing threshing vary, overall, there are no distinctive differences in harvest- ing operations. Cutting, gathering, and feeding mechanisms are essentially the same regardless of the type or model of combine used. Hoag (1972) studied the physical and mechanical proper- ties of soybean pod shattering. Hoag found that very little energy was needed to open soybean pods at impact velocities encountered at typical combine reel and cutterbar speeds. He reported a definite decrease in the amount of energy necessary to cause soybean shatter as the soybean moisture C