Temperature and low concentration effects of the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) on ammonia volatilization from urea

Abstract

The effect of the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) on urea hydrolysis and NH 3 volatilization was studied in laboratory experiments. At ambient laboratory temperatures. NH 3 volatilization rates were shown to be significantly reduced by an nBTPT concentration in urea as low as 0.005% (w/w). After 8 days, at ambient laboratory temperatures, NH 3 loss from urea was 37.7%. whereas losses from the 0.005 and 0.05% nBTPT products were 13.6 and 1.8%. respectively. Higher concentrations of nBTPT were required at 32°C than at 18°C to achieve equivalent suppression of NH, loss. A direct relationship was not observed between inhibition of urea hydrolysis and the concomitant reduction in NH 3 loss. After 4 days at ambient laboratory temperatures, 65% of untreated urea had been hydrolyzcd. whereas hydrolysis from the 0.01% product was 42%. Over the same period, NH 3 losses amounted to 12.3 and 1.8%, respectively. In the soils evaluated, effective inhibition of urea hydrolysis and NH 3 volatilization was obtained with very low concentrations of nNBPT, but higher concentrations were necessary at higher temperatures and in soils that had been amended with plant residues. The effect of nBTPT on loss may not have been due solely to delayed urea hydrolysis per se; rather, this delay may have also resulted in greater diffusion of urea into the soil and thus lowering the NH 3 concentrations at the microsites on the soil surface.