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Ammonia Volatilization from Nitrogen Sources Applied to Rice Fields: I. Methodology, Ammonia Fluxes, and Nitrogen‐15 Loss

1986; Wiley; Volume: 50; Issue: 1 Linguagem: Inglês

10.2136/sssaj1986.03615995005000010016x

1435-0661

I. R. P. Fillery, S. K. De Datta,

Groundwater and Isotope Geochemistry

Abstract The extent of NH 3 volatilization from (NH 4 ) 2 SO 4 , urea, and urea amended with the urease inhibitor, phenyl phosphorodiamidate (PPD), was studied concurrently in flooded rice ( Oryza sativa L.) by using nondisturbing micrometeorological techniques. Nitrogen‐15 balance techniques were used to estimate the total 15 N loss and the relative contribution of NH 3 volatilization and nitrification‐denitrification to the N loss. N sources were applied to the floodwater 18 d after the transplanting of rice seedlings (AT treatments). Ammonia volatilization proceeded rapidly after the application of (NH 4 ) 2 SO 4 and urea, although the pattern of NH 3 loss differed between the N sources. Ammonia fluxes accounted for 38 and 36% of the N applied as (NH 4 ) 2 SO 4 or urea, respectively, in an 8‐d period. A lower rate of NH 3 loss (22% N applied) occurred within the same period from a field amended with urea + PPD (1% wt/wt), primarily because NH 3 fluxes were negligible for at least 3 d after urea was applied. The total 15 N loss at the termination of the NH 3 loss measurements accounted for 44 and 41% of the (NH 4 ) 2 SO 4 and urea N, respectively. A significantly ( P ≦0.05) lower 15 N loss (33% N applied) occurred when a nitrification inhibitor (nitrapyrin) was applied with urea. These results suggested that nitrification‐denitrification may have contributed slightly to the total N loss from urea. Nitrapyrin did not significantly ( P <0.05) affect 15 N loss from microplots amended with (NH 4 ) 2 SO 4 . A simplified micrometeorological technique that used wind speed and atmospheric NH 3 concentrations at a single predetermined height to measure NH 3 fluxes accurately estimated fluxes ( R 2 = 0.99) that were determined by the horizontal flux or mass balance technique. An indirect estimate of NH 3 loss based on the rate of 15 N loss from nitrapyrin and urea amended microplots (33% N applied) was similar to the total NH 3 loss computed with the mass balance micrometeorological technique (36% N applied). This finding confirms the reliability of the mass balance micrometeorological technique used in NH 3 loss measurements.