Over a period of 28 days, NH3 loss from ***13N-labeled urea (100 kg N ha−1 on a pot area basis) applied to a presubmerged Guthrie silty clay loam (Typic Fragiaquult, pH 6.0 and cation exchange capacity of 15 cmol kg−1 soil) increased from 33 to 58% with an increase in airflow rate from 2.5 to 25 L min−1. Ammonia volatilization was a nonlinear function of the airflow rate because a proportional increase in NH3 loss with increasing airflow rate seemed to be reversed by lower temperatures (up to 5°C) and pH values (up to 1.5 units) of flood-water noticed at airflow rates of 15 to 25 L min−1. Algal growth was checked and urea hydrolysis was slowed with an increase in airflow rate. Gaseous loss of N via apparent denitrification varied from 13 to 17% (differences statistically nonsignificant) as the airflow rate decreased from 25 to 2.5 L min−1.
Leaching at a rate of about 4 mm d−1 reduced NH3 volatilization from 32 to 12% of applied N. Denitrification with leaching decreased the loss of 15N from 21 to 16%. Losses of 15N in the leachate were negligible (<0.5%). Presubmergence for 14 d compared with 3 d encouraged early algal growth, a faster urea hydrolysis, and a quick rise in pH, which enhanced N loss through NH3 volatilization during the first 4 days of urea application. Irrespective of airflow rate, the cumulative loss of N as NH3 increased with the duration of presubmergence, but N loss through denitrification was not affected. The overall results of this study suggest that fluctuations in N loss as NH3 from a flooded soil did not significantly influence the accompanying N loss through denitrification.