Mid‐ or late‐fall N fertilization is usually recommended on the Canadian prairies to reduce N losses from fall‐applied N. Yet, N fertilizers are less efficient when applied in mid‐ or late fall than in spring on crop yield. Ammonia volatilization from N fertilizers is one of the reasons for the low N use efficiency. We conducted a 2‐yr study to quantify and contrast the efficacy of a urease inhibitor, N‐(n‐butyl) thiophosphoric triamide (NBPT), with and without a nitrification inhibitor, 3,4‐ dimethylpyrazole phosphate (NI), in reducing NH₃ volatilization from fall‐ and spring‐applied urea‐based fertilizers in two contrasting soils. Treatments consisted of surface‐applied urea and urea–NH₄NO₃ (UAN) with and without NBPT or NBPT + NI (double inhibitor, DI). We measured NH₃ volatilization with acid‐charged disks during 21 (fall) or 28 (spring) d. Total NH₃ volatilization (percentage of applied N) from untreated urea and UAN across sites ranged from 7 to 22% with fall application and from 3 to 29% with spring application. Addition of NBPT only or DI to urea or UAN reduced NH₃ volatilization by 61 to 74% in the fall and 4 to 69% in the spring across site‐years. We found that the reduction of NH₃ volatilization by NBPT was significantly greater in the fall (65%) than in the spring (40%) and with urea (61%) than with UAN (43%). Our study showed that (a) significant NH₃ volatilization could occur from surface‐applied urea‐based fertilizers even under late‐fall temperatures and (b) NBPT reduced NH₃ volatilization from fall‐ as well as spring‐applied urea‐based fertilizers. Therefore, farmers are encouraged to treat their urea‐based fertilizers with NBPT when considering surface application.

中文翻译：

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尿素酶和硝化抑制剂处理的秋季尿素与春季尿素基肥料的效率I. NBPT的氨挥发和缓解

通常建议在加拿大大草原上施用中后期或后期氮肥，以减少秋季施用的氮素造成的氮素损失。然而，秋季中后期或秋季施用氮肥的效率低于春季。氮肥中的氨挥发是氮利用效率低的原因之一。我们进行了为期2年的研究，以量化和对比尿素酶抑制剂N-（正丁基）硫代磷酸三酰胺（NBPT），有和没有硝化抑制剂3,4-二甲基吡唑磷酸酯（NI）在还原中的功效在两种相反的土壤中，秋季和春季施用的尿素基肥料中的NH ₃挥发。处理包括表面施用的尿素和尿素-NH ₄ NO ₃（UAN）有和没有NBPT或NBPT + NI（双重抑制剂，DI）。我们在第21天（秋季）或第28天（春季）用带电荷的圆盘测量了NH ₃挥发。秋季施用时，未处理尿素和UAN的总NH ₃挥发量（施用的N百分比）在秋季施用时为7％至22％，在春季施用时为3％至29％。在整个站点年间，仅在尿素或UAN中添加NBPT或DI即可减少NH ₃挥发量，秋季减少61％至74％，春季减少4％至69％。我们发现，秋季（65％）比春季（40％）和尿素（61％）比UAN（43％）明显减少，NBPT减少的NH ₃挥发量更大。我们的研究表明（a）大量的NH ₃即使在晚秋温度下，表面施用的基于尿素的肥料也可能发生挥发，并且（b）NBPT减少了秋季施用的NH ₃和春季施用的尿素的肥料的挥发。因此，鼓励农民在考虑表面施肥时用NBPT处理其尿素基肥料。