Development and Validation of Alternate Wetting and Drying (AWD) Water Management for Rice Grown on Clay Soils in Mississippi.

Rice irrigation currently accounts for the greatest amount of irrigation water applied per acre over corn, soybeans, and cotton in the mid-south. The alluvial aquifer serves as the major source of irrigation water for rice production in Mississippi; however, it is declining at a rate of 300,000 acre feet per year and has done so for approximately 25 years. An experiment was conducted at the Delta Research and Extension Center in Stoneville, MS to evaluate the yield and physiological response of rice to several alternate wetting and drying (AWD) irrigation regimes. Three rice cultivars were evaluated in six different rice irrigation treatments. Irrigation treatments included: a continuous flood, allowing the flood to recede to the soil surface, 4” below the soil surface, 8” below the soil surface, 12” below the soil surface, and 16” below the soil surface. Water level in each paddy was monitored and irrigation events were triggered at each respective threshold back to a 4” flood, then allowed to subside until threshold was reached. Rice grain yield response of two AWD treatments were equal to rice grown with a continuous flood. A ten bushel grain yield increase was observed when the flood within a paddy was allowed to recede to the soil surface compared to a continuous flood. Grain yield for continuous flood was equal to rice grown with flood receding to 4” below soil surface. Reduction of grain yield was observed when the flood receded past 8” below the soil surface as compared to a continuous flood. Data from this experiment in 2015 suggest that allowing flood to subside to 4 inches below the soil surface does not result in yield loss compared to a continuous flooded system. Water management practices that reduce groundwater withdrawals are a viable option for rice producers in the mid-south.