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The Effect of Defoliants on Seed Quality of Soybean (GIycine max (L.) Merrill)
Thesis Abstract:
A greenhouse experiment was conducted at the Central Experiment Station of the University of the Philippines Los Baños (UPLB) to evaluate the effects of various defoliants (handpicking as control, sodium chlorate, 2, 4 D ester, and glyphosate) and time of application on soybean. The study also compared the effectiveness of the defoliants in accelerating harvest time.
Defoliants were applied at different stages of maturity: a) nearly all seeds have not reached their physiological maturity (when 90% of pods were still green); b) half of the seeds have already reached their physiological maturity (when 50% of pods became yellow); c) all of the seeds reached their physiologocal maturity (100% of pods became yellow); d) at post physiological maturity (when 90% of pods were yellow and the rest became brown).
Application of defoliants prior to physiological maturity signiftcantly reduced percent weed weight, gemination rate, vigor index, total dry weight of normal seedlings, and gave a higher percentage of abnormal seedlings. Application of defoliants at the time of physiological maturity and at post physiological maturity gave a higher percent seed weight, germination rate, vigor index, total dry weight of normal seedlings but a lower percentage of abnormal seedlings. Yield component such as the number of pods, productive branches, and nodes were not significantly affected by the application of defoliants. The only seed yield component affected by the application of defoliants was percent seed weight.
Compared with untreated plants. application of defoliants significantly reduced harvest age. Untreated plants needed 101 days from seed sowing to harvesting. The shortest harvest age (80 days) found was from application of sodium chlorate at the time when 90 percent of pods were still green. The application of glyphosate when most of the pods had become yellow gave the longest harvest age (93 days). The application of defoliants shortened harvest age the range of 8-21 days.
Application of 2, 4 D ester and glyphosate prior to physiological maturity resulted in higher abnormal seedlings exhibiting stunted hypocotyl, defective primary leaves, and terminal buds