Ammonia losses following surface application of enhanced-efficiency nitrogen fertilizers and urea

The so-called “enhanced-efficiency N fertilizers” were developed to mitigate ammonia losses from surface-applied urea (UR) and thereby increase N use efficiency and crop yield. However, research is needed to assess the efficiency of these products in mitigating ammonia emission. The aim of this study was to compare volatilization losses of ammonia following application of UR treated with B and Cu (B-Cu-UR), UR treated with dicyandiamide (DCD) and N-(n-butyl) thiophosphoric triamide (NBPT) (DCD-NBPT-UR), UR treated with humic substances (HS-UR), UR treated with NBPT (NBPT-UR), polymer S-coated UR (PSCUR), S-coated UR (SCUR), and untreated and uncoated UR (UR). Fertilizers (at a rate of 2355 mg N kg−1) were applied over the soil surface, and volatilized ammonia was quantified for 60 d under controlled conditions using a static closed chamber. Use of DCD-NBPT-UR increased ammonia emissions in comparison to UR by blocking nitrification and keeping the soil pH high, the latter resulting from UR hydrolysis. Urease complexation by the inhibitor and gradual N release resulted in low losses of ammonia by NBPT-UR and PSCUR, respectively. Compared to UR, BCu-UR delayed and slightly decreased ammonia volatilization. HS-UR, SCUR, and UR fertilizers had similar ammonia losses. Humic substances most likely did not act on urea-N complexation or even on decreasing urease activity, whereas immediate release of the nutrient by SCUR was noted. NBPT-UR and PSCUR could substitute for UR, aiming to mitigate ammonia volatilization.