Association of NBPT and Zinc Sources into Urea: A New Approach to Slow Down Nitrogen Releasing and Reduce Losses

Purpose: Urea is the nitrogen (N) fertilizer most used worldwide, however, when this N-fertilizer is broadcast over the soil surface, ammonia (NH₃) volatilization decreases nitrogen use efficiency (NUE) by the plants. The N-(n-butyl) thiophosphoric triamide (NBPT) is the urease inhibitor most used to mitigate NH₃ volatilization from urea. Although zinc (Zn) is also reported as a urease inhibitor, it is unknown the existence of synergy due to the association of both urease inhibitors into urea. Methods: Urea-based fertilizers were individually produced with three Zn sources: nanoparticles of ZnO_{(nanoscale, 30 nm)}, bulk ZnO_{(microscale ≥100 nm)} and zinc sulfate, hereafter named as Nano-ZnO, Micro-ZnO and ZnSO₄, respectively. Thereafter, regular (NBPT-Rgr) and reduced NBPT rates (NBPT-Rr) were associated with the fertilizers. Closed chambers were used to evaluate NH₃ volatilization from the fertilizers in two incubation trials. Cumulative NH₃ volatilization across the period in which the trials were performed was adjusted to a nonlinear model. Results: NBPT-Rgr and Nano-ZnO associated into urea reduced NH₃ volatilization up to 13% and the time for maximum NH₃ losses was delayed up to 19.4 days, as compared with the same parameters observed with urea application. Similarly, under NBPT-Rr and ZnSO₄ added into the fertilizers, NH₃ volatilization ranged between 8 and 10% and time for maximum NH₃ volatilization was delayed in 9 days. Moreover, ZnO added into N-fertilizers avoided abrupt soil pH increases as compared with ZnSO₄. Conclusion: When Nano-ZnO or ZnSO₄ plus NBPT are added into urea N releasing is slowed down. Therefore, both urease inhibitors combined into urea potentially enhances the N recovery efficiency from urea when this N-fertilizer is applied over the soil surface in the agroecosystems.