Nitrogen leaching losses from lysimeters containing winter kale: the effects of urinary N rate and DCD application

Nitrogen (N) leached from the plant‐soil system is an environmental concern. The objective of this study was to quantify N leaching losses from cow urine deposited during grazing of a winter forage crop (kale), and determine the effect of using the nitrification inhibitor dicyandiamide (DCD) to reduce N leaching losses. Fresh cow urine was applied to the surface of large soil monolith lysimeters in late June 2011 at two urinary N deposition rates; 500 and 700 kg N ha −1 (with and without DCD), and compared with losses from lysimeters receiving no urine. Most of the N leaching loss was in the form of nitrate‐N (NO 3 – ‐N), with an average of 25% leached as ammonium‐N (NH 4 + ‐N). Nitrate‐N leaching losses were significantly higher under urine‐treated lysimeters (213 and 380 kg NO 3 – ‐N ha −1 at the 500 and 700 kg N ha −1 rates, respectively) than those without urine (c. 33 kg NO 3 – ‐N ha −1 ). The application of DCD reduced NO 3 – ‐N leaching losses by up to 54%. The results indicate that N leaching losses from winter forage crop systems are high and that the application of DCD can reduce these losses.