Ammonia Volatilization from Flooded Soil Systems: A Computer Model. III. Validation of the Model
1990
Jayaweera, G. R. | Paw U., K. T. | Mikkelsen, D. S.
An NH₃-volatilization model predicting NH₃ loss as a function of five input variables was validated using a wind tunnel to simulate rice paddy conditions and direct field experiments. A total of five variables in a central composite statistical design were compared to study the interactive effects of NH₄-N concentration, pH, temperature, wind speed, and water depth. Experiments were also conducted in a flooded rice field with polypropylene basins placed at water level. Samples were collected every hour for determination of NH₄-N concentration. Temperature, pH, and wind speed were recorded continuously, and water depth was constant. Wind-tunnel data showed that the model predicted observed values with excellent accuracy in the range of conditions found in flooded rice systems. The regression of predicted NH₃ loss on observed losses resulted in an r² of 0.98 and a regression slope of 0.99. Field experiments also showed very close agreement between predicted and experimental values with 6-, 12-, and 24-h averages of pH, temperature, and wind speed. The model validation confirmed the theory that NH₃ volatilization is a function of NH₃(aq) concentration and the volatilization rate constant for NH₃, which are dependent on five variables: floodwater NH₄ concentration, pH, temperature, water depth, and wind speed. The model is theoretically sound and predicts NH₃ loss with a high level of accuracy using a menu-driven computer program with easily measurable variables, and can be used in comparison studies of NH₃ loss at the same site. Contribution from the Dep. of Agronomy and Range Science and the Dep. of Land, Air, and Water Resources, Univ. of California, Davis.
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