Evaluation of soil urease and nitrification inhibitors

The growing importance of urea fertilizer in world agriculture has stimulated extensive research to find compounds that will retard hydrolysis of urea by soil urease and thereby reduce gaseous loss of ;Most of the fertilizer N applied to soils is in the form of ammonium or ammonium-producing compounds such as urea. The nitrate formed through nitrification of this fertilizer N by soil microorganisms is susceptible to loss by leaching and denitrification. The adverse effects of oxidation of ammonium to nitrate by the nitrifying microorganisms in soil have stimulated research to find compounds that can be used as fertilizer amendments to retard nitrification of fertilizer N. Studies to evaluate compounds showing the most promise as soil nitrification inhibitors demonstrated that their effectiveness decreased in the order: 2-ethynylpyridine ;Studies of the relationships between the structures of heterocyclic N compounds and their effectiveness of inhibition of nitrification in soil showed that unsubstituted heterocyclic N compounds containing two adjacent ring N atoms inhibit nitrification in soil and that two of these compounds, pyrazole and 1,2,4-triazole, are potent inhibitors. They also showed that several substituted pyrazoles and thiadiazoles are effective soil nitrification inhibitors. (Abstract shortened with permission of author.).