Physiological Quality of Soybean Seeds Affected by Water and Light Deficits

In order to determine the best developmental stage of soybean at which maximum seed quality is attained under different shadings (S1, S2, S3: 0, 35 and 75% shade, respectively) and irrigation treatments (I1, I2, I3, I4: irrigation after 60, 90, 120 and 150 mm evaporation from class A pan, respectively), two split plot experiments using randomized complete block design with three replications were conducted in 2011 and 2012. Seeds were harvested at five day intervals in eight stages. Maximum seed weight (mass maturity) was achieved at 41-54 days after flowering. Seed filling duration decreased with decreasing water supply, but it was increased by shading. As a result, maximum seed weight, germination rate and seedling dry weight of seeds from shaded plants were higher than those of unshaded plants. However, minimum electrical conductivity and maximum germination percentage of seeds from shaded and unshaded plants under different irrigation treatments were almost similar. Maximums of seed quality parameters were obtained 1 to 9 days after mass maturity, depending on the light availability and irrigation intervals. At earlier harvests, because of immaturity, and at later harvests, due to aging, seed physiological quality was low. It was concluded that high quality seeds of soybean can be produced under different irrigation and shading treatments, providing that the seeds are harvested at about 16-20% moisture content.