Water Table Management, Nitrogen Dynamics, and Yields of Corn and Soybean

Concern about NO − 3 contamination of surface waters has prompted the development of agricultural water table management systems to reduce NO − 3 loss in subsurface drainage outflow by subirrigating through the existing subsurface drainage lines during the growing season and controlling off‐season outflows. We hypothesized that soil N pools, crop yields, and N uptake in a corn ( Zea mays L.)–soybean ( Glycine max. ) rotation differ between subirrigation (water table at 40 cm) with controlled drainage (SI/CD) vs. subsurface drainage (SD) alone on Omulga silt loam (Aeric Fragiaqualfs). Mean microbial biomass N, potentially mineralizable N, dissolved organic N, and ammonia N were not affected by the water table management system. Mean NO − 3 –N was not affected by the water table management system at 0‐ to 15‐cm and 15‐ to 30‐cm depths, but the 2‐yr mean soil NO − 3 concentration at the 30‐ to 75‐cm depth was 46% lower in SI/CD compared with SD. The average corn yield was 19% greater, and the average soybean yield was 64% greater, in SI/CD plots, compared with SD. Corn N uptake was 13% greater and soybean N uptake was 62% greater with SI/CD, compared with SD. The SI/CD water table management system increased plant N uptake and reduced deep‐profile NO − 3 concentrations, thereby reducing the amount of NO − 3 potentially available to move via drains to surface waters.