Efficiency of fall versus spring applied urea‐based fertilizers treated with urease and nitrification inhibitors I. Ammonia volatilization and mitigation by NBPT
2020
Lasisi, Ahmed A. | Akinremi, Olalekan O. | Zhang, Qiang | Kumaragamage, Darshani
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.
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