Effects of shallow water tables on soil aeration, water quality, and physiological growth of soybean

摘要

This study was conducted to investigate the effects shallow water table depths on soil aeration, groundwater quality and on some physiological growth and yield parameters of soybean. The experiments were conducted in two environmentally controlled growth chambers using sixteen lysimeters. Water table (WT) treatments were established on 37 day after planting (DAP), at depths of 0.15-, 0.30-, 0.45- and 0.60-m below the soil surface. Soil aeration status was determined by measuring soil oxygen concentrations at 0.15-, 0.30-, 0.60-m depths in the lysimeters. Effects of water table depths on groundwater quality were determined by observing the movement of residual soil nitrate and applied metolachlor at three different depths (0.20-, 0.40-, and 0.60-m) in the soil profile. Measurements on different physiological parameters (photosynthesis rate, stomatal conductance, transpiration rate, chlorophyll content and intercellular CO[subscript]2) and leaf temperature were taken on a weekly basis;The results of study showed that oxygen concentration was significantly reduced by raising the water table depth. Differences in soil oxygen concentrations for various soil depths were also significant. Soil oxygen concentration at shallow soil depths was always higher compared to deeper soil depths. The variation in soil oxygen concentrations with time was not significant. Significant reductions in both NO[subscript]3-N and metolachlor concentrations were observed by maintaining shallow WT depths. For 0.15-m WT treatment, the NO[subscript]3-N and metolachlor concentrations were 54 and 63%, respectively, lower compared to 0.60-m WT treatment. The analysis of drainage outflow data also supported the fact that shallow WT treatments can reduce the leaching of NO[subscript]3-N and metolachlor to groundwater. A week after the establishment of WT treatments, different physiological parameters of soybean were significantly affected. Photosynthesis rate, stomatal conductance and transpiration rates were significantly reduced when WT was raised to 0.15-m depth. Soybean yield was significantly reduced with the decrease in WT height. The results of this study indicate that, on the average, 48% increase in yield is possible by maintaining WT at 0.60-m depth.