Fertilizer Nitrogen Movement During Four Days of Surface Water Ponding.
Peter J. Tomlinson, Mary C. Savin, David M. Miller, Kristofer R. Brye, and Richard J. Norman. Crop, Soil and Environmental Sciences Dept., University of Arkansas, 115 Plant Science Building, Fayetteville, AR 72701
Previously, urea N moved deeper into silt-loam soil than ammonium sulfate N when ponded with water for up to 12 hours. Since fields remain flooded, we extended the time that water was maintained on the soil surface from 12 to 96 hours to determine if movement of N from the two fertilizers diverged to a greater extent with time. Furthermore, because it can take up to a week to flood a rice field, the effects of a 5-day delay in flood establishment and the use of a urease inhibitor treated-urea fertilizer (Agrotain) on N movement were examined. Urea or ammonium sulfate was dissolved on the surface of intact DeWitt silt-loam soil cores (approximately 10 cm length) that were ponded with water for 12 to 96 hours. Ammonium-N concentrations were measured in flood water and at 2-cm depth intervals in the soil cores. When there was no delay in ponding establishment, N in soil amended with ammonium sulfate was greatest at the surface 2 cm, decreased with depth, and was not significantly affected by ponding duration. In contrast, after 96 hours of ponding, N in soils amended with urea was similar from 0 - 4 cm. Ponding duration also significantly affected N concentrations measured at depths below 4 cm; N increased from 12 to 96 hours. Following a 5-day delay in ponding, N concentrations in urea amended cores were greatest at the surface 2 cm of soil and decreased with depth. After 96 hours of ponding, N in soil amended with Agrotain was consistent with N in soil receiving urea that had no delay in ponding. The type of fertilizer and time until flooding impact the depth of N movement within the surface 10 cm of soil during 96 hours of surface water ponding.