THE FATE OF FRESH AND STORED N-15-LABELED SHEEP URINE AND UREA APPLIED TO A SANDY AND A SANDY LOAM SOIL USING DIFFERENT APPLICATION STRATEGIES

The fate of nitrogen from N-15-labelled sheep urine and urea applied t o two soils was studied under field conditions. Labelled and stored ur ine equivalent to 204 kg N ha(-1) was either incorporated in soil or a pplied to the soil surface prior to sowing of Italian ryegrass (Lolium multiflorum L.), or it was applied to ryegrass one month after sowing . In a sandy loam soil, 62% of the incorporated urine N and 78% of the incorporated urea N was recovered in three cuts of herbage after 5 mo nths. In a sandy soil, 51-53% of the labelled N was recovered in the h erbage and the distribution of labelled N in plant and soil was not si gnificantly different for incorporated urine and urea. Almost all the supplied labelled N was accounted for in soil and herbage in the sandy loam soil, whereas 33-34% of the labelled N was unaccounted for in th e sandy soil. When the stored urine was applied to the soil surface, 2 0-24% less labelled N was recovered in herbage plus soil compared to t he treatments where urine or urea were incorporated, irrespective of s oil type. After a simulated urination on grass, 69% of the labelled ur ine N was recovered in herbage and 15% of the labelled N was unaccount ed for. The labelled N unaccounted for was probably mainly lost by amm onia volatilization. Significantly more urine- than urea-derived N (36 and 19%, respectively) was immobilized in the sandy loam soil, wherea s the immobilization of N from urea and urine was similar in the sandy soil (13-16%). The distribution of urine N, whether incorporated or a pplied to the soil surface prior to sowing, did not influence the immo bilization of labelled urine N in soil. The immobilization of urine-de rived N was also similar whether the urine was applied alone or in an animal slurry consisting of labelled urine and unlabelled faecal N. Wh en urine was applied to growing ryegrass at the sandy loam soil, the i mmobilization of urine-derived N was significantly reduced compared to application prior to sowing. The results indicated that the net miner alization of urine N was similar to that of urea in the sandy soil, bu t only about 75% of the urine N was net mineralized in the sandy loam soil, when urine was applied prior to sowing. Thus, the fertilizer eff ect of urine N may be significantly lower than that of urea N on fine- textured soils, even when gaseous losses of urine N are negligible.