Ammonia Volatilization from Nitrogen Sources Applied to Rice Fields: I. Methodology, Ammonia Fluxes, and Nitrogen-15 Loss1
- I. R. P. Fillery and
- S. K. De Datta2
The extent of NH3 volatilization from (NH4)2SO4, 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 15N loss and the relative contribution of NH3 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 (NH4)2SO4 and urea, although the pattern of NH3 loss differed between the N sources. Ammonia fluxes accounted for 38 and 36% of the N applied as (NH4)2SO4 or urea, respectively, in an 8-d period. A lower rate of NH3 loss (22% N applied) occurred within the same period from a field amended with urea + PPD (1% wt/wt), primarily because NH3 fluxes were negligible for at least 3 d after urea was applied. The total 15N loss at the termination of the NH3 loss measurements accounted for 44 and 41% of the (NH4)2SO4 and urea N, respectively. A significantly (P ≦0.05) lower 15N 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 15N loss from microplots amended with (NH4)2SO4. A simplified micrometeorological technique that used wind speed and atmospheric NH3 concentrations at a single predetermined height to measure NH3 fluxes accurately estimated fluxes (R2 = 0.99) that were determined by the horizontal flux or mass balance technique. An indirect estimate of NH3 loss based on the rate of 15N loss from nitrapyrin and urea amended microplots (33% N applied) was similar to the total NH3 loss computed with the mass balance micrometeorological technique (36% N applied). This finding confirms the reliability of the mass balance micrometeorological technique used in NH3 loss measurements.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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