Evaluation of Selected Processes Controlling Nitrogen Loss in a Flooded Soil

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Abstract
The roles of NH4‐N diffusion, NH4‐N oxidation, NO3‐N diffusion, and NO3‐N reduction in controlling N loss from continuously flooded soil were evaluated in independent experiments. Applied NH4‐N moved from zones of high NH4‐N concentration to the zones of low NH4‐N concentration. The average diffusion coefficient (D) for NH4‐N in flooded soil ranged from 0.059 to 0.216 cm2 day−1 for different soils. Diffusion coefficients were influenced by soil type and soil‐water content. Rate of NH4‐N oxidation in the aerobic layer of flooded soil range from 1.2 to 3.5 µg g−1 day−1 in different soils. Nitrate diffusion into the anaerobic soil layer ranged from 0.96 to 1.91 cm2 day−1, whereas NO3‐N reduction rates were 0.32 to 0.52 day−1. The slow rate of NH4‐N diffusion from the anaerobic soil layer to the aerobic soil layer and the slow rate of NH4‐N oxidation in the aerobic soil layer indicate that these two processes are limiting steps in controlling N loss. Nitrate diffusion into the anaerobic soil layer and NO3‐N reduction in the anaerobic soil layer were found to proceed at a faster rate and are not likely to limit N loss from flooded soil.

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