The leaching of nitrogen from surface-applied fertilizer to groundwater is an environmental concern. Nitrogen fertilizer is routinely applied to turfgrass from spring to late autumn in Canada. The main objective of this study was to determine the contribution of N applied in May, July and September to leaching. The leaching of applied chloride (May and September only) was also monitored and the transport of nitrate and chloride were simulated using the model LEACHM (within EXPRES) to assist in fulfilling the main objective. The accuracy of the model simulation for transport, not nitrogen losses, was also addressed. Field lysimeters (Guelph, Ontario) were packed with a three-horizon profile of a sandy loam soil, topped with Kentucky bluegrass (Poa pratensis) sod and monitored for 1 year. Based on soil water samples taken from suction samplers placed at depths of 10, 17, 29, 43, 54, 64 and 85 cm, part of the solute from spring/summer applications remained in the soil during the unusually dry summer. This residual solute was later transported downward with the ensuing infiltration front in late autumn, building upon the autumn application, resulting in excessive concentrations. Predictions by LEACHM of solute concentration profiles generally were similar to field measurements.

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