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

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.

Effect of Straw Application on Rice Yields and Nutrient Availability on an Alkaline and a pH-neutral Soil in a Sahelian Irrigation Scheme

“…This suggests an increase in NH 3 volatilization rate in straw treatments. Bouldin et al (1991) reported that increased urea hydrolysis with straw application (Sahrawat 1983;Gill et al 1999;Pattnaik et al 1999) resulted in increased floodwater NH 4 + concentrations and enhanced NH 3 volatilization losses. Furthermore, if volatilization decreased as a result of straw application, we should have observed a negative interaction for the factors C · S on NH 4 + peak concentrations, but the increase in NH 4 + peak concentrations upon straw application was equal or higher in C treatments when compared to the no C treatments.…”

Effect of Soil Water Contents on Urea Hydrolysis and Nitrification in a Newly Reclaimed Tidal Soils

“…The differences in the accumulation of nitrate among different soil moisture contents represented that rates of urea hydrolysis was influenced by increasing volumetric water content due to increased diffusion of urea to the urease enzyme as investigated by Bouldin et al (1991). Katyal and Carter (1988) also found that increased hydrolysis rates were closely related with increasing time of submergence.…”

Improving Efficiency of Urea Fertilizers by Inhibition of Soil Urease Activity

“…Hongprayoon et al (1991) and Bouldin et al (1991) studied urea transformations in flooded soil columns. A silt loam soil (pH in H20 5.8) collected from the Rice Research Station in Crowley (Louisiana) was used.…”