Direct Measurement of Ammonia and Denitrification Fluxes from Urea Applied to Rice uri icon

abstract

  • Ammonia volatilization and denitrification are widely reported to be mechanisms of fertilizer-N loss from lowland rice fields, but few researchers have simultaneously measured NH3 and denitrification losses from applied N in order to ascertain the relative importance of these two mechanisms. Ammonia volatilization and denitrification losses from urea broadcast into 0.05-m-deep floodwater at 11 d after transplanting were directly measured at a lowland irrigated site at Calauan, Laguna, Philippines. Ammonia loss was measured by the mass-balance micrometeorological technique in two dry seasons (1986 and 1988), and denitrification loss was measured from evolution of (N2 + N2O)-N-15 into a confined chamber during the 20 d following application of N-15-labeled urea in two dry seasons (1987 and 1988). Ammonia loss was 54 and 46% of the applied urea-N during the 8 d following N application in 1986 and 1988, respectively. Recovery of evolved (N2 + N2O)-N-15 was 0.1% of the applied urea-N in both 1987 and 1988. Total N loss, determined from unrecovered N-15 in N-15 balances at 20 d after urea application, was 64, 43, and 52% of the applied N in 1986, 1987, and 1988, respectively. Denitrification loss, determined by the difference between total N loss and directly measured NH3 loss, was 10 and 6% of the applied urea-N in 1986 and 1988, respectively. Estimates of denitrification tended to be greater with the difference method (10 and 6%) than with the direct recovery of (N2 + N2O)-N-15 (< 1%). Nonetheless, NH3 volatilization was consistently the dominant mechanism of gaseous N loss from broadcast urea.

publication date

  • 1991
  • 1991
  • 1991