Greenhouse Study on the Effects of the Urease Inhibitors Phenyl Phosphorodiamidate and N‐(n‐butyl) Thiophosphoric Triamide on the Efficiency of Urea Applied to Flooded Rice

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Abstract
Urea was split applied to transplanted rice in a greenhouse experiment with two‐thirds applied as labeled15N urea at 15 days after transplanting (DAT) and one‐third (not labeled) at 42 DAT to determine the effect of the urease inhibitors phenyl phosphorodiamidate (PPDA) and N‐(n‐butyl) thiophosphoric triamide (NBPT) on urea hydrolysis, plant uptake, yield, and loss of fertilizer N. An acidifying agent [Al2(SO4)3] and an algicide were used to reduce the floodwater pH and thus slow the degradation of PPDA, keeping it effective for a longer period. Algicide addition extended the effectiveness of PPDA inhibition by about 2 days and increased plant uptake and grain yield significantly over that with urea use alone. Al2(SO4)3addition extended the effectiveness of PPDA only about 1 day, increased N uptake slightly, but failed to increase grain yield. NBPT effectively slowed urea hydrolysis, more than doubled plant uptake over that with urea alone, and increased grain yield by 38%. Percolation at 0.5 cm per day caused plant N uptake to increase by about 6% in all treatments but it was not essential for the inhibitors to have a beneficial effect. For the first split application, fertilizer losses of 50% from urea were decreased to about 10% by use of NBPT and to 28% with PPDA alone, and by combination of PPDA with the algicide losses were 22%.