2012 Volume 38 Issue 5 Pages 290-298
Behaviors of nitrogen compounds were investigated to elucidate the mechanisms of nitrogen (N) removal in a forage rice field applied with liquid cattle waste (LCW). In total, 567 kg-N·ha−1 of NH4-N was applied to the rice field by basal fertilization and three applications of LCW topdressing as supplemental fertilizer during the cultivation period. The N balance (calculated from NH4-N and NO2+3-N leaching, nitrous oxide (N2O) and ammonia (NH3) emissions, nitrogen uptake by rice plant and N adsorption into the soil) showed that almost 80% of the input N was taken up by plants and removed via denitrification during the cultivation period, while 11.7% of input N remained as adsorbed N in the soil at harvest. Increases in NO3-N concentration in the soil solution and N2O fluxes after drainage indicated that the drainage procedure is important for enhancement of nitrification and denitrification. Nitrogen removal rates after LCW application were estimated by the box model and suggested that declining nitrogen uptake rate by rice plants after the 3rd LCW application caused the remnant N in the soil at harvest. These results suggest that an appropriate schedule and amount of LCW application could be effective to reduce remnant N.