The influence of hydroxamates on ammonia loss from an acid loamy sand treated with urea

Abstract

In a laboratory investigation of the volatilization of ammonia following the application of urea to an acid loamy sand it was found that the loss of ammonia could be delayed for several days and the maximum rate of loss could be reduced by the addition to the soil of various monohydroxamic acids. All the hydroxamic acids used are non-competitive inhibitors of the enzyme urease but in the soil system caprylo-hydroxamic acid and phenylaceto-hydroxamic acid were ineffective in retarding ammonia loss and on a molar basis acetohydroxamic acid (AHA) was a more effective inhibitor than either benzo-, capro- or salicylohydroxamic acid. The effectiveness of AHA in delaying ammonia loss was proportional to its concentration at any one concentration of urea. AHA added to soil several days before the application of urea did not delay losses of volatile ammonia. This may have been due either to chemical inactivation or biological decomposition of AHA or to the proliferation of ureaseforming organisms tolerant towards AHA. When either sulphanilamide, copper sulphate or sodium diethyldithiocarbamate were added to the soil they caused slight delays in ammonia loss but they were far less effective than AHA. The delay caused by AHA treatment was prolonged in the presence of sulphanilamide and this effect was attributed to toxic effects of sulphanilamide on urease-forming organisms.