Water table management, nitrogen dynamics, and yields of corn and soybean

Concern about NO3- contamination of surface waters has prompted the develop ment of agricultural water table management systems to reduce NO3- loss in subsurface drainage outflow by subirrigating through the existing subsurfac e drainage lines during the growing season and controlling off-season outfl ows. 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 dra inage (SD) alone on Omulga silt loam (Aeric Fragiaqualfs), Mean microbial b iomass N, potentially mineralizable N, dissolved organic N, and ammonia N w ere not affected by the water table management system, Mean NO3--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 NO3- concentration at the 30- to 75-cm de pth was 46% lower in SI/CD compared with SD, The average con yield was 19% greater, and the average soybean yield was 64% greater, in SI/CD plots, com pared with SD. Corn N uptake was 13% greater and soybean N uptake was 62% g reater with SI/CD, compared with SD. The SI/CD water table management syste m increased plant N uptake and reduced deep-profile NO3- concentrations, th ereby reducing the amount of NO3- potentially available to move lia drains to surface waters.