Several workers have reported that O2has little, if any, effect on hydrolysis of urea by soil urease, but others have reported that it has a marked effect, hydrolysis being significantly faster in soils under aerobic conditions than in O2-depleted soils. In studies to account for these divergent results, we found that whereas plant residues and other readily decomposable organic materials markedly stimulated microbial production of urease in soils under aerobic conditions, they did not greatly stimulate production of urease in soils under anaerobic conditions. We also found that although anaerobic conditions retarded production of urease by soil microorganisms, they did not inhibit hydrolysis of urea by soil urease. These observations suggest that the divergent findings concerning the effect of O2on hydrolysis of urea by soil urease may have resulted from differences in the amounts of readily decomposable organic materials in the soils studied.
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