The fate of 15N from dairy cow urine under pasture receiving different rates of N fertiliser

N-15-labelled urine was used to study the fate of N applied as urine in spring, summer and autumn on ryegrass receiving two different fertiliser rates (100 and 300 kg N . ha(-1) . yr(-1)) in Brittany (France). Ammonia volatilisation of labelled urine N was less than 4% and immobilised urine N represented 21 - 31% of the applied N-15. Recovery of labelled N in plants ranged from 30 to 65% of N input as urine, showing a decrease in autumn for the highest fertiliser nitrogen treatment. The plant recovery of urine N was relatively high in autumn (49%) when urine was deposited on ryegrass receiving a fertiliser rate of 100 kg N . ha(-1) . yr(-1). Lower N fertiliser regimes can therefore lower the leaching potential of urine N in pastures.