NITROGEN AND PHOSPHORUS FLUXES FROM A FLOODED ORGANIC SOIL

Abstract

Under laboratory conditions, we measured nitrogen and phosphorus fluxes from an anaerobic organic soil to the overlying water. In the anaerobic soil layer, ammonification was functioning at a rate of 0.11 g N/m2-day, and NH4+ flux from the anaerobic soil layer to the floodwater and to the aerobic soil layer was 0.045 g N/m2-day. The sequential N processes functioning in a flooded organic soil include: ammonification in the anaerobic soil layer, upward diffusion of NH4+ from the anaerobic soil layer to the floodwater, nitrification in the floodwater, downward diffusion into the anaerobic soil layer and denitrification in the anaerobic soil layer. Losses due to these processes accounted for about 35 percent of the mineralized NH4+-N in the 21-cm organic soil column. Results also showed that ammonification and NH4+ diffusion functioning at a slower rate probably are the limiting processes in N loss from a flooded organic soil. The results also showed that the rate of soluble P production in the anaerobic soil layer was 0.016 g P/m2-day, and the flux of P, as a result of diffusion, was about 0.0098 g P/m2-day. Major processes functioning in the anaerobic layer were mineralization of organic P, adsorption-desorption of P, and diffusion from underlying sediment to the overlying water. Losses of P due to these processes accounted for about 53 percent of the solubilized P in the 21-cm organic soil column.