Rate control of ammonia volatilization from rice paddies

Abstract

As part of a research program aimed at improving the efficiency of fertilizer N in flooded rice, an assessment is being made of the losses of NH 3 by volatilization. A model was developed to analyze the influence of floodwater chemistry and meteorological conditions. The complicated process of ammonia transfer across the gas-liquid interface was described using this model in conjunction with current theories of chemical reaction kinetics, evaporation from natural waters and atmospheric boundary layers. The model was shown to approximate with fair accuracy a data set obtained in a laboratory wind-water tunnel, simulating rice paddy conditions. Results of the analysis show the rate of ammonia volatilization to increase with increasing ammoniacal-N concentrations and pH of the floodwater as well as wind velocity and temperature, while it decreased with increasing fetch. The effects of wind, temperature and pH on the rate of ammonia volatilization are of the same order of magnitude. Some practical implications of the results are discussed.