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Ammonia Volatilization from Nitrogen Sources Applied to Rice Fields: I. Methodology, Ammonia Fluxes, and Nitrogen-15 Loss¹

ABSTRACT

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.

¹ Contribution from the Agro-Economic Division, International Fertilizer Development Center (IFDC), P.O. Box 2040, Muscle Shoals, AL 35662; and the International Rice Research Institute (IRRI), P.O. Box 933, Manila, Philippines.

² Formerly Soil Scientist, IFDC, and Visiting Scientist, Dep. of Soil Chemistry, IRRI; and Head, Dep. of Agronomy, IRRI, respectively. Present address of senior author, Dryland Crops and Soils Research Programme, CSIRO, Private Bag PO, Wembley, WA 6014, Australia.

Received for publication July 11, 1984. Accepted for publication August 9, 1985.