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Wind-tunnel Simulation and Assessment of Ammonia Volatilization from Ponded Water¹

Several techniques for the prediction of ammonia volatilization rates from rice paddies are evaluated using experimental data obtained in a wind-water tunnel, set up to simulate rice paddy conditions.

The wind tunnel results suggest that nonuniform surface conditions of waters with short fetch do not significantly limit the use of aerodynamic techniques for the prediction of ammonia volatilization rates. Comparison of volatilization rates predicted with a one-dimensional aerodynamic technique as well as a two-dimensional modification of this technique against those predicted from the longitudinal ammonia flux at the downwind section of a wind-water tunnel yield differences on the order of 10%.

Ammonia volatilization rates and aqueous chemistry measured under small enclosures are compared with those measured in the wind-water tunnel. The results indicate that quantitative assessment of ammonia volatilization losses in the field is possible if air exchange rates in the enclosure are selected which yield a gas phase resistance representative of average wind conditions.

Key Words: Rice paddies • Flooded soils • Micrometeorology • Aerodynamic techniques

² Assistant professor, Dep. of Civil Engineering, Michigan State Univ., East Lansing, Michigan, formerly affiliated with Dep. of Civil Engineering, Colorado State Univ., Fort Collins, Colorado, and soil scientist, Agro-Economic Div., Intern. Fert. Devel. Ctr., respectively.

Received for publication July 8, 1980.