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Increasing concentrations of nitrate-N (NO3 -- N) in surface and subsurface water resources are a major concern where livestock manures are being land applied. A five year field experiment to examine NO3 -- N losses to subsurface drains was carried out, and two applications of liquid dairy manure under different conditions were examined. The first surface application of liquid manure increased NO3 -- N concentrations in the subsurface drains from an average of 7 mg L-1 prior to the manure, to 9.6 mg L-1 after the manure was applied. However, when the liquid manure was incorporated immediately after a surface application, no increases in NO3 -- N concentrations were observed following this manure application. Preferential flow processes were observed to influence the forms of nitrogen lost and the initial amounts. When the liquid manure was surface applied, the NO3 -- N concentration in the drainage effluent increased rapidly to a concentration similar to that in the liquid manure, and provided the majority of the initial N load. Plow incorporation of the liquid manure had the greatest effect on reducing ammonium-nitrogen concentrations in the drainage effluent.