A Visual Indicator of the Physiological Maturity of Soybean Seed1

Abstract

The objective of this study was to identify a visual indicator of the physiological maturity (PM) of soybean (Glycine max [L.] Merrill) seeds. Six soybean cultivars with different seed colors at maturity were grown in the field for 2 years, and the date of maximum seed dry weight accumulation at nodes seven, eight, and nine was determined. Visible seed, pod and leaf charactexistics throughout the maturation process were recorded. Maximum seed dry weight occurred when the seeds had an average of 58% moisture. Of the 11 selected visible criteria, the one that coincided consistently with the determined date of PM was the initiation of seed shrinkage. The complete loss of green color from the pod was also a reliable indicator of PM since it always occurred in the sampling period immediately following observed seed shrinkage. Because the determined date of PM in this study could have been slightly premature, the loss of green color in the pods might be considered the better indicator of seed PM. Loss of green color from the pods would be a convenient and rapid field determination of PM.