15N recoveries from ruminant urine patches on three forage types

Abstract

15Nitrogen balances are useful tools to increase our understanding of soil N processes and the efficiency of plants in taking up animal urine-N. This study aimed to investigate the effect of forage type on the fate of autumn-applied urine-N (700 kg N ha−1). In a 17-month lysimeter study the recoveries of 15N in herbage, leachate, nitrous oxide, and soil + roots (at the end of the trial) were determined for three forage types: perennial ryegrass-white clover (RGWC, Lolium perenne L.-Trifolium repens L.), Italian ryegrass (Italian RG, Lolium multiflorum Lam.), and lucerne (Medicago sativa L.) under simulated autumn grazing. We recovered 81.5–85.5% of the 15N applied in the urine. Italian RG had the greatest amount of urine-15N recovered in the herbage (49.5%) and the least recovered in leachate (16.8%) making it the most efficient of the three forages for utilizing urine-N. For RGWC, herbage and leachate recoveries were 40.1% and 23.7%, respectively. Lucerne was the least efficient with recoveries of 15N in herbage and leachate equaling 18.4% and 52.5%, respectively. This study demonstrates that Italian ryegrass could offer benefits in reducing urine-N leaching losses through its ability to take up more urine-N over winter.