Wheat Yield and Nitrogen Utilization Efficiency Affected by Urea Coated with NBPT Urease Inhibitor and Environmental Conditions in Brazilian Rhodic Oxisols

Urea is the main nitrogen (N) fertilizer used in the wheat crop, but it is susceptible to volatilization losses. These losses can be reduced by urease inhibitors such as N-(n-butyl) thiophosphoric triamide (NBPT). This study evaluated wheat yield and N utilization efficiency (NUtE) of the cultivar BRS Gralha-Azul in response to N levels, to urea coated with different levels of NBPT, to the timings of N fertilization, and to environmental conditions experienced in-season in Brazilian Rhodic Oxisols. The experiment was carried out in three environments: Londrina under rainfed and irrigated conditions, and Ponta Grossa under rainfed conditions. Agronomic features related to N plant nutrition and wheat yield were assessed. Environmental conditions determined the effectiveness of N fertilization and NBPT on NUtE and grain yield. In Londrina, irrigation improved the density of fertile spikes and the N concentration and N accumulation in shoot dry matter, which contributed to increase grain yield by 39%. Nitrogen fertilization increased NUtE for shoot dry matter production in all the environments, and reduced NUtE for grain yield only in Londrina under rainfed conditions. NBPT is not effective under acid soil conditions combined with high water availability. Nitrogen fertilizer applied only at sowing may be enough for the spring wheat crop to achieve its yield capacity in subtropical environments. The management of N fertilization and NBPT can be improved if the historical data on environmental features throughout the wheat-growing season are considered. An alternative for increasing grain yield under drought conditions is to improve plant N uptake by increasing the N concentration in the soil solution via N fertilization. The optimal level of NBPT for coating urea depends on the N fertilizer level applied to wheat crop, as well as on the timing of N fertilization. Thus, the most suitable procedure for wheat farmers would be to customize the NBPT level according to their specific environmental conditions and N fertilization management practices, instead of purchasing N fertilizer with a single NBPT level.