Lysimeter study of the fate of nitrogen in animal urine returns to irrigated pasture

Summary The fate of 15 N‐labelled synthetic urine (50 g N m −2 ) applied to an irrigated pasture soil was studied using large undisturbed monolith lysimeters (800 mm diameter × 1200 mm deep). Over a period of 1 year, the pasture plants recovered the largest fraction of the applied 15 N (43%) and approximately 20% of the applied 15 N still remained in the soil, the majority of which was found in the topsoil (0–20 cm). Although the experiment was conducted under relatively intense rainfall and irrigation conditions, only 8% of the applied 15 N was found to have leached below 1200 mm after 1 year. During this time, the average peak concentration of nitrate in the leachate reached 42 mg NO 3 − ‐N dm −3 . The amount of nitrogen (N) lost by the process of denitrification was calculated as 28% of the applied 15 N. This large loss of N to the atmosphere was attributed to the wet soil conditions which prevailed.