Hayashi Kentaro, Nishimura Seiichi, Yagi Kazuyuki
Carbon and Nutrients Cycles Division, National Institute for Agro-Environmental Sciences, 3-1-3, Kan-nondai, Tsukuba, Ibaraki 305-8604, Japan.
Sci Total Environ. 2008 Feb 15;390(2-3):485-94. doi: 10.1016/j.scitotenv.2007.10.037. Epub 2007 Dec 3.
Ammonia (NH(3)) volatilization from a paddy field following applications of urea was measured. Two lysimeters of Gray Lowland soil with a pH (H(2)O) of 5.7 were used for the experiment. Urea was applied at a rate of 50 kg N ha(-1) by incorporation as the basal fertilization (BF) and at rates of 30 and 10 kg N ha(-1) by top-dressing as the first (SF1) and second (SF2) supplemental fertilizations, respectively. Two wind tunnels per lysimeter were installed just after BF; one was transplanted with rice plants (PR plot), and the other was without rice plants (NR plot). Weak volatilization was observed at the PR plots after BF. By contrast, strong volatilization was observed at the PR plots after SF1 with a maximum flux of 150 g N ha(-1) h(-1); however, almost no volatilization was observed after SF2. The NH(3) volatilization loss accounted for 2.1%, 20.9%, 0.5%, and 8.2% of the applied urea at each application, BF, SF1, SF2, and the total application, respectively, for which only the net fluxes as volatilization were accumulated. The NH(3) volatilization fluxes from the paddy water surface (F(vol)) at the NR plots were estimated using a film model for its verification. After confirmation of good correlation, the film model was applied to estimate F(vol) at the PR plots. The NH(3) exchange fluxes by rice plants (F(ric)) were obtained by subtracting F(vol) from the observed net NH(3) flux. The derived F(ric) showed that the rice plants emitted NH(3) remarkably just after SF1 when a relatively high rate of urea was applied, although they absorbed atmospheric NH(3) in the other periods. In conclusion, rice plants are essentially an absorber of atmospheric NH(3); however, they turn into an emitter of NH(3) under excess nutrition of ammoniacal nitrogen.
测定了施用尿素后稻田中氨（NH₃）的挥发情况。使用了两个pH（H₂O）为5.7的灰低地土壤渗漏计进行实验。作为基肥（BF），尿素以50 kg N ha⁻¹的用量通过混入土壤施用；作为第一次追肥（SF1）和第二次追肥（SF2），分别以30 kg N ha⁻¹和10 kg N ha⁻¹的用量进行表施。在基肥施用后，每个渗漏计立即安装两个风洞；一个种植水稻（PR小区），另一个不种植水稻（NR小区）。基肥施用后，在种植水稻的小区观察到较弱的氨挥发。相比之下，第一次追肥后，在种植水稻的小区观察到强烈的氨挥发，最大通量为150 g N ha⁻¹ h⁻¹；然而，第二次追肥后几乎没有观察到氨挥发。氨挥发损失分别占每次施肥（基肥、第一次追肥、第二次追肥）以及总施肥量下施用尿素的2.1%、20.9%、0.5%和8.2%，这里仅累积了作为挥发的净通量。使用薄膜模型估算了非种植水稻小区稻田水面的氨挥发通量（F(vol)）以进行验证。在确认具有良好相关性后，将薄膜模型应用于估算种植水稻小区的F(vol)。通过从观测到的氨净通量中减去F(vol)得到水稻植株的氨交换通量（F(ric)）。推导得到的F(ric)表明，在施用相对高用量尿素后的第一次追肥后，水稻植株显著释放氨，尽管在其他时期它们吸收大气中的氨。总之，水稻植株本质上是大气氨的吸收者；然而，在氨态氮营养过剩的情况下，它们会变成氨的排放者。
