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This article in SSSAJ

  1. Vol. 55 No. 2, p. 543-548
    Received: Nov 8, 1989

    * Corresponding author(s):
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Direct Measurement of Ammonia and Denitrification Fluxes from Urea Applied to Rice

  1. S. K. De Datta ,
  2. M. I. Samson,
  3. W. N. Obcemea,
  4. J. G. Real and
  5. R. J. Buresh
  1. Agronomy-Physiology-Agroecology Division, International Rice Research Inst. (IRRI), P.O. Box 933, 1099 Manila, Philippines
    International Fertilizer Development Center (IFDC), P.O. Box 2040, Muscle Shoals, AL 35662



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 loss 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)-15N into a confined chamber during the 20 d following application of 15N-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)-15N was 0.1% of the applied urea-N in both 1987 and 1988. Total N loss, determined from unrecovered 15N in 15N 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)-15N (<1%). Nonetheless, NH3 volatilization was consistently the dominant mechanism of gaseous N loss from broadcast urea.

Joint contribution from IRRI and IFDC.

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