LAUSR

Correspondence Thort Chuong, Dep. of Plant Sciences, Univ. of California, Davis, CA 95616, USA. Email: [email protected] Abstract Ammonia volatilization, a primary N loss pathway from rice (Oryza sativa L.) production systems, leads to a reduction in N use efficiency and environmental problems. Ammonia volatilization has not been studied in water-seeded rice systems or where aqueous NH3 is the primary fertilizer N source. Our objective was to quantify NH3 volatilization from preplant aqueous NH3 and compare it with drilled or broadcast urea. In addition, NH3 volatilization from a topdress N application applied midseason was quantified. This was accomplished with 10 field experiments representing a range of soil types. Preplant N treatments were a zero-N control, injected aqueous NH3, broadcast urea, and drilled urea all applied at the farmer application rate to a dry soil. For the topdress experiment, the treatments were a zero-N control and urea or (NH4)2SO4 applied at 34 kg N ha −1. Ammonia volatilization was measured up to 3 and 1 wk after the preplant and topdress N was applied, respectively, using a semi-open static chamber. Losses due to NH3 volatilization from preplant broadcast urea were significantly higher than from the other other treatments but accounted for <2% of applied N. Losses from aqueous NH3 and banded urea were lower but were significantly greater than from the control. The losses occurred in the first week after flooding. When N was topdressed, 1.5 and 2.6% of applied N were lost via volatilization from urea and (NH4)2SO4, respectively.