Leaching losses of nitrogen from sheep urine patches

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Abstract
The fonns and amounts of urine nitrogen (N) leached under unsaturated flow conditions were compared for both undisturbed soil monolith lysimeters (500 mm diam. X 340 mm deep) and laboratory columns of pre-sieved (<2 mm), repacked soil. A comparison of breakthrough curves indicated that different flow mechanisms operated in each. Leaching of urine through undisturbed soillysimeters produced total N concentrations up to 1003 mg/litre within the first 0.1 pore volume of drainage, declining rapidly thereafter. Extensive' preferential flow through earthwonn channels and other macropores was suggested to be the main mechanism for such rapid leaching. In contrast, N levels in leachate collected from repacked soil columns indicated a complete lack of preferential flow pathways. Over 10% of the applied urine N was leached after only 0.2 pore volumes of drainage (c.27mm) had occurred from the undisturbed soil lysimeters.