The effectiveness of herbicidal desiccants and application times on seed yield and earliness of soybean

Abstract

Two herbicidal desiccants and five application times at different reproductive stages of soybean were investigated for earliness without significant reduction in seed yield and quality. Glyphosate and diquat were applied to soybean cv. ‘Arısoy’ (maturity group III) at growth stages of R5, R6, R7 and R8. Full maturity (FM) and uprooted plants at each growth stage were also used as a control. Plant height, first pod height, pod number per plant, seed weight per plant, thousand seed weight, seed yield and oil ratio were investigated. The results showed that plant height was not affected by desiccants and application times. Lower seed weight per plant, thousand seed weight, seed yield, and oil ratio were obtained from earlier reproductive stages, especially at R5, and R6, but glyphosate produced higher seed yield and oil content than diquat. Both desiccants considerably reduced seed yield when applied at R5 and R6. Mean seed yield enhanced from 1,364 to 3,036 kg ha-1 in first year and from 1,097 to 2,804 kg ha-1 in second year as the growth stages extended from R5 to R8. Diquat was more effective desiccant for accelerating soybean harvest than glyphosate, while higher seed yield was obtained from glyphosate spraying at R5 and R6 stages. Increased seed yield was observed in diquat application when the soybean growth stages were delayed from R5 to R8. It was concluded that glyphosate should be applied at R7 in soybean for earliness with 7-10 days in harvest and no desiccant should be suggested before R7 stages.