Microbial decomposition of 2-oxo-4-methyl-6-ureidohexahydropyrimidine in soil

The microbial decomposition of 2-oxo-4-methyl-6-ureidohexahydropyrimidine (CDU), a slow-release nitrogenous fertilizer, in soil, and its N release were investigated by the soil perfusion method with a soil which had received yearly applications of CDU for 5 yr. The decomposition of CDU proceeded in two steps with an initial lag and intermediate stagnation period, and total decomposition was complete in 24 days in the first perfusion culture. In subsequent perfusions. CDU was decomposed without lags within less than 3 days. Urea and NH₄⁺ were released during CDU decomposition.Two species of CDU-decomposing bacteria were isolated from perfused soil. Both grew well in a medium containing CDU as a sole source of carbon and nitrogen, and released urea and NH⁺₄, but each species could decompose only 50% of the CDU supplied. One could decompose the (−)CDU isomer and the other the (+)CDU isomer. They were identified as members of the genera Arthrobacter and Corynebacterium, respectively.The relationship of the CDU-decomposition pattern to the growth of these two species of bacteria in the soil perfusion cultures was demonstrated. It is suggested that the growth of the two species may contribute to the slow-release behaviour of CDU in soils which have a history of CDU application.