Effects of substituted p-benzoquinones on urease activity in soils

Abstract

The effectiveness of substituted p-benzoquinones as inhibitors of urease activity in soils depends largely upon their substituent groups. Methyl, chloro-, bromo- and fluoro-substituted p-benzoquinones have a marked inhibitory effect on soil urease activity, whereas phenyl-, r-butyl-and hydroxy-substituted p-benzoquinones have little, if any, effect. Methyl-substituted p-benzoquinones differ from other substituted p-benzoquinones in that their effects on soil urease activity usually increase markedly with increase in their time of contact with soil. A study of the effects of selected substituted p-benzoquinones on urea hydrolysis and volatilization of urea N as ammonia in a sandy soil treated with urea showed that methyl- and chloro-substituted p-benzoquinones had very marked effects, whereas hydroxy- and phenyl-substituted p-benzoquinones had little or no effect. Gaseous loss of urea N as ammonia when this soil was incubated at 20°C for 14 days was reduced from 62.8 to 0.1 per cent by addition of 2,3-dimethyl-, 2,5-dimethyl-, or 2,6-dimethyl- p-benzoquinone (2.3 parts/100 parts of urea). The work reported indicates that, of the 34 substituted p-benzoquinones studied, 2,3-dimethyl-, 2, 5-dimethyl- and 2,6-dimethyl- p-benzoquinone are likely to prove the most effective for retardation of urea decomposition in soils and reduction of the problems caused by the normally rapid hydrolysis of fertilizer urea by soil urease.