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Apparent Persistence of N ‐( n ‐butyl) Thiophosphoric Triamide Is Greater in Alkaline Soils
Author(s) -
Engel R.E,
Williams E.,
Wallander R.,
Hilmer J.
Publication year - 2013
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2012.0380
Subject(s) - loam , chemistry , alkali soil , soil water , urea , volatilisation , ammonia volatilization from urea , environmental chemistry , alkaline hydrolysis , soil ph , urease , hydrolysis , nuclear chemistry , soil science , biochemistry , organic chemistry , geology
Recently completed NH 3 volatilization field studies with urea suggest the urease inhibitor N ‐( n ‐butyl) thiophosphoric triamide (NBPT) has prolonged activity in alkaline relative to acidic soils. A laboratory incubation experiment was conducted at two temperatures (0.5 and 20°C) to determine whether NBPT degradation was affected by soil pH (alkaline vs. acidic) and to determine the impact on urea hydrolysis. Soil (10 g) from the surface horizon of a loam (pH 5.5) and a silt loam (pH 8.4) was placed in bottles and incubated up to 28 d in constant‐temperature chambers. A third soil was constructed by adding CaCO 3 (0.3 g) to the loam soil (pH 8.2). Urea (20 mg) with and without NBPT (20 mg) was applied to each soil. High‐performance liquid chromatography–mass spectrometry analysis of KCl extracts revealed that NBPT degraded rapidly in the acidic soil compared with the alkaline soils (silt loam and loam with added CaCO 3 ). Exponential decay constants for the acidic soil were 5.2 and 3.9 times larger than decay constants for the alkaline soils at 0.5 and 20°C, respectively. Urea hydrolysis rates were reduced by NBPT, and the response was greater for the alkaline soils ( P < 0.0001). Hydrolysis was inhibited by 17.0 and 86.2% at 20°C and by 53.3 and 92.1% at 0.5°C for the acidic and alkaline soils, respectively. This study confirmed field observations that NBPT persistence and activity is greater in alkaline soils. Additional studies, including chemical hydrolysis and sorption, are needed to clarify the processes responsible for the rapid disappearance of NBPT from extracts of acidic soils.