Effect of drying conditions and harvest time on soybean seed viability and deterioration under different storage temperature

Quality attributes of seeds may decline during storage. Quantifying loss of seed germination during storage has given rise to an equation proposed by Ellis and Roberts that, “same rate of seed deterioration will take place among seed lots of a species in identical environments”. This study was conducted to determine whether deterioration will take place at the same rate, and also to evaluate the factors that affect rate of deterioration. Storage experiments were performed in three constant temperatures of 15, 20 and 25°C and seed moisture contents of 12% using 32 soybean seed lots (cv. Williams) obtained from different harvest date and dried in various combinations of drying. The GENMOD procedure of SAS was used for analysis of standard germination of seed lots, and stepwise regression was used to simulate effects of pretreatment conditions plus storage temperature on seed viability during storage. Data analysis with separate and parallel lines showed that equation of Ellis and Roberts is not applicable for these seeds. Trend of germination reduction were plotted, slops of curves were analyzed and correlated with variables. Harvest moisture, its interaction with storage temperature and second order of harvest moisture had the most effects on rate of deterioration. The moisture content had adverse effect on this rate and interactions of storage temperatures with drying temperature intensify that in higher temperature. Also, high drying temperatures, air velocity, and deep loading exacerbate this rate. Trends of electrical conductivity (Ec) increment that can be related to lipid peroxidation, chemical change or membrane disturb confirmed the results.   Key words: Seed deterioration, seed quality, soybean seed and seed viability.