Transformations of 15N labelled urea in different types of soil

Soils of different origins (Belgium, Cameroon and the Sudan) were used to study the transformations of labelled urea N. It was found that, in all soils, the hydrolysis of urea occurred within a few days of its application at 25 deg. C. Under aerobic conditions and with no additional organic matter, between 25 and 38% of the urea applied to the tropical soils (from the Sudan and Cameroon) was in the organic pool after one month of incubation. The corresponding amount in the Belgian soils was only about 10%. Addition of organic matter stimulated immobilization of urea N. Some differences were observed in the rate and extent of urea N transformations under aerobic and anaerobic conditions. Addition of urease inhibitors retarded the urea hydrolysis and increased urea N immobilization. It was found that N-(n-butyl)phosphorothioic triamide was more effective than phenylphosphorodiamidate and hydroquinone. (author). 24 refs, 7 tabs