Responses of seed yield, quality, and composition to the harvest-aid paraquat in soybean grown in Mississippi

Authors: Bellaloui, Nacer; Smith, James - Rusty; Ray, Jeffery - Jeff; Mengistu, Alemu; Gillen, Anne; Fisher, Daniel; SINGH, GURBIR - Mississippi State University

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2022
Publication Date: 4/26/2022
Citation: Bellaloui, N., Smith, J.R., Ray, J.D., Mengistu, A., Gillen, A.M., Fisher, D.K., Singh, G. 2022. Responses of seed yield, quality, and composition to the harvest-aid paraquat in soybean grown in Mississippi. Agrosystems, Geosciences & Environment. 5(2):e20262. https://doi.org/10.1002/agg2.20262.
DOI: https://doi.org/10.1002/agg2.20262

Interpretive Summary: Paraquat is a herbicide that can be used in soybean as a harvest-aid to desiccate green tissues for harvest efficiency and for maintaining seed quality. However, its application can cause significant crop damage if applied too early. Information on the effects of paraquat, or herbicides in general, as a desiccant on seed quality and seed damage is almost non-existent. Therefore, the objective of this study was to investigate the impact of the timing of paraquat application on soybean seed yield, seed quality (germination and viability), seed damage, and seed protein, oil, and sugars. A field experiment using two soybean cultivars (P46A57BX and P48A60X) was conducted in 2019 and 2020 at Stoneville, MS, USA. Paraquat was applied at the recommended rate at growth stages R6 (full seed-fill), R6.5 (pod cavities completely filled with seeds), and R7 (yellow color/beginning maturity). Results showed that application of paraquat at R6 resulted in yield loss in two years for both cultivars. Seed germination and viability were also reduced, but only in one year. No seed damage that would result in dockage was observed in any treatment, as seed damage in all treatments was below 2%. Application of paraquat at R6 resulted in significantly higher protein, oleic acid, raffinose, and stachyose, but lower oil and sucrose. Application of paraquat at R6.5 resulted in yield loss for both cultivars in both years, whereas application at R7 resulted in significant yield loss for P46A57BX in both years, but in only one year for P48A60X. This research demonstrated that the harvest-aid paraquat reduced seed yield even when applied beyond the R6.5 growth stage, indicating that some seeds in pods were still filling beyond R6.5. Therefore, producers using harvest-aids for harvest efficiency may also reduce yield if the product is applied too early.

Technical Abstract: Paraquat can be used as a harvest-aid to desiccate green tissues for harvest efficiency and for maintaining seed quality. However, its application can cause significant crop damage if applied too early. Therefore, the objective of this study was to investigate the impact of the timing of paraquat application on soybean seed yield, seed quality (germination and viability), seed damage, and seed protein, oil, and sugars. A field experiment was conducted in 2019 and 2020 at Stoneville, MS, USA. Paraquat was applied at a rate of 0.56 kg ai ha-1 at growth stages R6 (full seed-fill), R6.5 (pod cavities completely filled with seeds), and R7 (yellow color/beginning maturity). Cultivars P46A57BX and P48A60X were used. Results showed that application of paraquat at R6 resulted in yield loss in two years for both cultivars. Seed germination and viability were also reduced, but only in one year. No seed damage that would result in dockage was observed in any treatment, as seed damage in all treatments was below 2%. Application of paraquat at R6 resulted in significantly higher protein, oleic acid, raffinose, and stachyose, but lower oil and sucrose. Application of paraquat at R6.5 resulted in yield loss for both cultivars in both years, whereas application at R7 resulted in significant yield loss for P46A57BX in both years, but in only one year for P48A60X. This research demonstrated that the harvest-aid paraquat reduced seed yield even when applied beyond the R6.5 growth stage, indicating that some seeds in pods were still filling beyond R6.5. Therefore, producers may use harvest-aids for harvest efficiency, but they may also reduce yield if applied too early.