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Urea Transformations in Flooded Soil Columns: II. Derivation of Model and Implications to Ammonia Volatilization

Soil, Crop and Atmospheric Sciences Dep., Cornell Univ., Ithaca, NY 18453

C. Hongprayoon and W. H. Patrick, Jr.

Lab. for Wetland Soils and Sediments

C. W. Lindau^*

Lab. for Wetland Soils and Sediments and Nuclear Science Center, Louisiana State Univ., Baton Rouge, LA 70803

*Corresponding author.

ABSTRACT

Ammonia volatilization from rice (Oryza sativa L.) paddies following urea application reduces the effectiveness of the urea-N. The objectives of this study were to: (i) derive, for flooded soils, a model describing hydrolysis and diffusion of urea and diffusion of ammoniacal N; (ii) derive the necessary parameters from experimental data, and (iii) use the model to study implications of hydrolysis/transport parameters and management variables to NH₃ volatilization. The parameters are diffusion coefficients of urea and NH₄ in soil, hydrolysis coefficients of urea in the soil and overlying floodwater, and the sorption coefficient for NH₄ on the soil. The effects on potential for NH₃ volatilization of variation in these parameters and the management factors of depth of flood water and depth of fertilizer incorporation were calculated. The results illustrate that urea-hydrolysis rates in the floodwater and soil are the most important factors influencing the potential for NH₃ volatilization. If urea-hydrolysis rates are very high, incorporation and shallow floodwater are the indicated management while, with low hydrolysis rates, deep floodwater and no incorporation are the indicated management.

Cornell Paper no. 1741.

Received for publication September 18, 1990.