Nitrogen (N) fertilizer retention and short-term vertical redistribution into soil affect N balance and N-use efficiency in rice (Oryza sativa L.) production systems. A series of experiments was conducted on intact soil cores obtained from rice production fields to track floodwater and soil ammonium- and nitrate-N concentrations up to 96 hr after urea and ammonium sulphate fertilizer amendments to dry, silt loam soil (a) as compared to clay soil, (b) with and without a delay before floodwater establishment and (c) at two initial soil water conditions (dry and muddy). The impact of a 5-day delay before flood establishment was also compared between untreated and N-(n-butyl)thiophosphoric triamide (NBPT)-treated urea-N concentrations. Urea-derived N generally moved deeper into dry, silt loam soil than ammonium sulphate. Ammonium sulphate-derived N concentration was greatest in the surface 2 cm of soil, decreased with depth, and was unaffected by floodwater duration. A 5-day delay between fertilization and flooding resulted in urea behaving similarly to ammonium sulphate, although NBPT treatment resulted in vertical N distributions similar to those for untreated urea applied to dry, immediately flooded soil. When urea was applied to muddy soil, no fertilizer N was observed below 2 cm, while large concentrations of ammonium-N remained in the floodwater. Results collectively demonstrate the importance of immediate downward movement of fertilizer-applied N into dry soil for retention, and the use of a urease inhibitor to maximize urea-derived N downward movement into soil when a delay in flood establishment cannot be avoided.

中文翻译：

---

水稻生产用粉砂壤土和黏土的地表水驱化肥氮的垂直分布

氮 (N) 肥料保留和短期垂直重新分配到土壤中会影响水稻 ( Oryza sativa L.) 生产系统中的氮平衡和氮利用效率。在从水稻生产田获得的完整土壤核心上进行了一系列实验，以追踪在尿素和硫酸铵肥料添加到干燥粉砂壤土后 96 小时内的洪水和土壤铵和硝酸盐 N 浓度（a）与粘土，(b) 在洪水形成之前有和没有延迟，(c) 在两种初始土壤水条件下（干燥和泥泞）。还比较了未处理和N -( n-丁基）硫代磷酰三胺（NBPT）处理的尿素-N浓度。尿素衍生的 N 通常比硫酸铵更深地迁移到干燥的粉砂壤土中。硫酸铵衍生的 N 浓度在土壤表层 2 cm 处最大，随深度降低，不受洪水持续时间的影响。施肥和淹水之间的 5 天延迟导致尿素的行为类似于硫酸铵，尽管 NBPT 处理导致垂直 N 分布类似于施用于干燥、立即淹水的土壤的未处理尿素的垂直分布。当尿素施用于泥质土壤时，在 2 cm 以下未观察到肥料 N，而洪水中仍有大量铵态氮。结果共同证明了施肥后立即向下移动到干燥土壤中以保留的重要性，