EFFECT OF ORGANIC-MATTER AND UREASE INHIBITORS ON UREA HYDROLYSIS AND IMMOBILIZATION OF UREA NITROGEN IN AN ALKALINE SOIL

Laboratory incubation experiments with N-15-labelled urea were conducted on a Aquic Udifluvent Belgian soil amended with barley straw, in order to study the influence of three urease inhibitors, hydroquinone, phenyl phosphorodiamidate and N-(n-butyl) phosphorothioic triamide on urea hydrolysis and N transformations. The results demonstrated that the urea was hydrolyzed more rapidly when the soil was amended with ground barley straw. A pronounced inhibition of urease inhibitors occurred with the urea hydrolysis, but it was decreased by increasing the soil organic C content. A severe N immobilization (about 82-100% of the applied urea) occurred in soil samples that were rich in organic C. The addition of urease inhibitors increased urea-N immobilization by 5-30%. N-(n-butyl) phosphorothioic triamide had a stronger effect than the other two inhibitors when they were applied at the rate of 1%. However, the inhibitors decreased N immobilization when the soil was amended with barley straw.