Optimization of soybean (Glycine max Merr.) seed drying conditions with response surface methodology in a constant-bed dryer using two cultivars

Abstract

Under wet and humid environmental conditions soybean seeds (Glycine max Merr.) are harvested early to avoid deterioration from weathering, otherwise, careful post-harvest drying would be required to maintain the physiological quality of seeds. Response Surface Methodology (RSM) was used to optimize the operating conditions of soybean seeds drying. The study was performed using a three-levels, four-factor fractional factorial design and aimed to determine the optimum combination of initial moisture content (X1), drying air temperature (X2), air velocity (X3), and depth of loading (X4) that could result a minimum number of cracked grains and high germination, quality and vigour attributes. The seeds of two soybean cultivars, i.e., Williams and JK with initial moisture content of 15 to 45% d.b, were dried in different drying air temperatures varied from 35 to 55°C, air velocity ranging from 0.5 to 1.5 m/s and different loading depth of 0.5 to 10 cm. According to the results, for cv. Williams the optimum drying conditions for seeds obtained at air temperature of 47°C, which need to be decreased with higher initial moisture content. Harvest can be started at about 35% initial seed moisture content, if drying was done carefully. But cv. JK was more susceptible and the drying air temperature not to be more than 40°C and harvesting would be started when the seed reach initial moisture content about 28% or less. Moreover, it is strongly recommended to use moderate depths of loading because of best aeration and air circulation and avoiding to overdrying. The seed quality indices in this experiment were more sensitive to both air temperature and initial moisture content than air velocity and depth of loading.