Rate and mode of application of the urease inhibitor N‐(n‐butyl) thiophosphoric triamide on ammonia volatilization from surface‐applied urea

Abstract

AbstractA laboratory study evaluated the effect of rate (0, 100, 250, 500, 750 or 1000 mg/kg) and mode of application of the urease inhibitor N‐(n‐butyl) thiophosphoric triamide (nBTPT) (coating the urea granule, adding to the urea melt or adding to urea ammonium nitrate (UAN) solutions) on NH3 volatilization from urea, at three temperatures (5, 15 and 25 °C), with four contrasting soil types. Daily ammonia loss was measured for up to 21 days after surface N application, using ventilated soil enclosures. Ammonia loss from unamended urea varied with soil type and temperature and ranged from 8.2 to 31.9% of the N applied. nBTPT was highly effective in lowering NH3 volatilization from urea and in delaying the time of maximum rate of loss. The average % inhibition over all soils, temperatures and formulations was 61.2, 69.9, 74.2, 79.2 and 79.8% for the 100, 250, 500, 750 or 1000 mg/kg nBTPT concentration, respectively. The % inhibition with nBTPT was lower at 15 °C compared with at 5 or 25 °C and was lower in UAN solutions than in granular products. There was little difference between the melted and coated granular products in lowering NH3 loss or in soil N transformations. The stability of nBTPT in urea products was dependent on its mode of application and on the storage temperature. Incorporating nBTPT in the urea melt produced a more homogeneous product with superior stability than coating the urea granule.