Soybean Tolerance To Waterlogged Soils

Too much water on soybeans is often worse than not having enough. Field yield maps usually show that soybean yields are lowest in the "wet spots". To manage irrigation more effectively, farmers need soybean varieties that can tolerate short periods of soil waterlogging. With conventional soybean varieties, farmers must mentally weigh each decision to make an irrigation application against the chance that a heavy rain will occur afterwards. In 2001, an experiment was begun screening soybean varieties for waterlogging tolerance at the Delta Center. Shown below were the most tolerant varieties to flooding at bloom growth stage. In 2003, a second study was started to determine what growth stage soybeans are most sensitive to waterlogging. Five selected varieties were flooded for an eight-day period at either V5 vegetative stage, Bloom, or Pod fill. We also conducted tests on different soils to determine how long soybeans can tolerate water before yields start to decline. Flood lengths included 0, 2, 4, 6, and 8 days. We found that even the most tolerant varieties were injured when extended soil waterlogging occurred. But the magnitude of yield loss was much less in the tolerant varieties compared to non-tolerant varieties. Yields were reduced from more than 48 hours for Delsoy 4710, a non-waterlog tolerant variety. Yields from P94B73 (one of the most tolerant varieties) lasted 96 hours of flooding before yields declined on both Sharkey clay and Tiptonville silt loam soils. The greatest yield loss from flooding for all varieties occurred at pod fill (R5). Injury also occurred at flooding at full bloom. The least injury occurred from flooding during V5 vegetative stage. We found that unless the early flooding killed the young plants, they were able to recover and produce 55 to 60 bushels per acre.