A comparison of the sulfur and oxygen analogs of phosphoric triamide urease inhibitors in reducing urea hydrolysis and ammonia volatilization

Abstract

A variety of compounds have been tested as urease inhibitors with the goal of providing a means of reducing ammonia volatilization losses from urea fertilizers when they are applied to the soil surface. Four phosphoric triamide compounds were studied in laboratory experiments to assess their effect on urea hydrolysis, soil ammonium levels, and ammonia volatilization. The compounds N(n-butyl) thiophosphoric triamide (nBTPT), cyclohexyl thiophosphoric triamide (CHTPT), and their oxygen analogs [N-(n-butyl) phosphoric triamide (nBPT) and cyclohexyl phosphoric triamide (CHPT), respectively] were mixed with urea at 0.1% and 0.01% w/w ratios, and the products were applied to the soil surface. A forced-draft apparatus was used to measure ammonia loss. The urea treatment lost 47% of applied N as ammonia in 14 d. The inhibitors applied at 0.1% w/w showed losses of 7%–10% in 14 d; at 0.01%, losses ranged from 13%–30% in the same period. At the 0.1% level, no significant difference was found among the inhibitors in terms of ammonia loss or urea hydrolysis trends. At the 0.01% concentrations, the oxygen analogs showed better urea urease inhibition than did the thio compounds, and their ammonia losses were half those of their sulfur analogs.