¹⁵N recoveries from ruminant urine patches on three forage types

Abstract

Background and aims: 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). Methods: 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. Results: 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. Conclusions: 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.