Soil properties and the ability of the urease inhibitor N-(n-BUTYL) thiophosphoric triamide (nBTPT) to reduce ammonia volatilization from surface-applied urea

• Published in: Soil biology & biochemistry Vol. 26; no. 9; pp. 1165 - 1171
• Main Authors: Watson, C.J., Miller, H., Poland, P., Kilpatrick, D.J., Allen, M.D.B., Garrett, M.K., Christianson, C.B.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.09.1994; New York, NY Elsevier Science
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Nitrogen fertilization; Nitrogen, phosphorus, potassium fertilizations; Soil-plant relationships. Soil fertility. Fertilization. Amendments; British Isles; Laboratory study; Nitrogen fertilization; Chemical analysis; Enzyme; Enzyme inhibitor; Property of soil; Urease; Ammonia; Urea; Amendment; Soil testing; Nitrogen cycle; Controlled environment study; Volatilization; Hydrolases; Inhibition; Organic thiotriamidophosphate; Nitrogen fertilizer; Grassland soil
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/0038-0717(94)90139-2

A laboratory study was made to evaluate the ability of the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) to reduce NH 3 volatilization from surface-applied urea. Urea was amended with 0.0, 0.01, 0.058 or 0.28% nBTPT (w/w) and was applied, at a rate equivalent to 100kgN ha −1, to the surface of 16 grassland soils, selected to show a wide range of different chemical and physical characteristics. Daily NH 3 loss was measured for 9 days, after fertilizer application, using ventilated enclosures at 13°C. The influence of soil properties on the effectiveness of nBTPT as a urea amendment was investigated using a modelling approach followed by stepwise multiple regression analysis. NH 3 volatilization from unamended urea ranged from 5.8 to 38.9% of the N applied and was greatest from a soil with a high pH and low titratable acidity. The % inhibition of NH3 loss by nBTPT was highly dependent on soil type, being effective on some soils even at the 0.01% nBTPT level. The % inhibition at the 0.28% level ranged from 99.4 to 54.4%. Modelling the relationship between total NH 3 loss and inhibitor concentration showed that the % nBTPT required to achieve a given % decrease in NH3 volatilization was constant for all soils. For example, 0.092% nBTPT was predicted to lower total NH3 loss by 90% from any given soil. The response to increasing inhibitor concentration in lowering NH 3 volatilization was greatest in a soil with low organic matter content and high pH. Stepwise multiple regression analysis showed that 4 soil properties (titratable acidity, pH-H 2O, urease activity and cation-exchange capacity) contributed significantly to explaining 90.6% of the variation in total NH 3 loss. In all soils the % urea remaining at the end of the incubation was 2.6, 4.6, 10.9 and 25.5% for 0.00, 0.01, 0.058 and 0.28% nBTPT, respectively. The persistence of urea treated with nBTPT was particularly marked in soils with a high pH and could have physiological implications for plants. It is particularly interesting that nBTPT was most effective in soils which showed high NH 3 volatilization from unamended urea.