Effect of biuret content on transformation of urea nitrogen in soil

The effect of the biuret content (0.0, 1.0, 2.5, 5.0 and 10.0% of urea) on transformations of urea-N was studied in a sandy loam (pH 7.7). While biuret did not affect urea hydrolysis, it inhibited the conversion of NH+4 to NO−2 and the subsequent oxidation of NO−2 to NO−3. This resulted in the accumulation of larger amounts of both NH+4-N and NO−2-N in soil as compared to soil receiving urea alone. The results suggest that biuret impurity in urea fertilizer is likely to enhance nitrite toxicity. ∗Present address: Soil Chemistry Department, International Rice Research Institute, Los Baños (Mail address: P.O. Box 933, Manila, Philippines), Philippines