Agronomic efficiency of NBPT as a urease inhibitor: A review

Abstract

Urea is the most widely used nitrogen (N) fertilizer, with a projected increase in annual demand of 1.5% in the coming years. After its application to soil, urea undergoes hydrolysis via the urease enzyme, causing increases in the soil pH in the surrounding area of the granules and resulting in NH₃ losses that average 16% of N applied worldwide and can reach 40% or more in hot and humid conditions. The use of urease inhibitors is an effective way to reduce NH₃ losses. Several compounds act as urease inhibitors, but only N-(n-butyl) thiophosphoric triamide (NBPT) has been used worldwide, being the most successful in a market that has grown 16% per year in the past 10 years. Only in the past three years other compounds are being commercially launched. In comparison to urea, NBPT-treated urea reduces NH₃ loss by around 53%. Yield gain by NBPT usage is of the order of 6.0% and varies from -0.8 to 10.2% depending on crop species. Nitrification inhibitors usually increase NH₃ volatilization and mixing them with urease inhibitors partially offsets the benefits of the latter in reducing NH₃ loss. The efficacy of NBPT to reduce NH₃ loss is well documented, but there is a need for further improvement to increase the period of inhibition and the shelf life of NBPT-treated urea.

Keywords: Ammonia volatilization; NBPT; NPPT; Nitrogen fertilizer; Nutrient use efficiency; Soil urease; Urea.

Graphical abstract

Fig. 1

Daily (A) and cumulative (B) ammonia volatilization losses after urea application with urease (NBPT) and nitrification (DCD) inhibitors. Reprinted from Soares et al. , with permission from Elsevier.

Fig. 2

Cumulative NH₃ loss during 42 d after application of urea and urea treated with N-(n-butyl) thiophosphoric triamide (NBPT). The points of the curves correspond to the arithmetic average of daily cumulative NH₃ loss compiled from 35 studies. The dash-dotted lines (urea) and dotted lines (urea + NBPT) represent (X axis) the number of days that elapsed for 20, 50, and 75% of the total NH₃ losses to occur. The R² value was 0.99 for both the urea and the urea + NBPT models. Reprinted from Silva et al. with permission from The American Society of Agronomy.

Fig. 3

Total NH₃ loss of urea and urea + NBPT (left) and the average reduction in NH₃ loss by treating urea with NBPT in comparison to untreated urea (right) considering the selected studies presented in Table 1-S of the Supplementary Material.

Fig. 4

Average yield increase per crop by treating urea with NBPT in comparison to the untreated urea, considering the selected studies presented in Table 2-S of the Supplementary Material. Error bars (right) represent the maximum and minimum values found in the original studies.