Assessment of a Large Subsurface Controlled Drainage and Irrigation System: II. Water Chemistry of the Tile Effluent and Its Potential Impact On Surface Water Resources.

Controlled subsurface drainage irrigation systems promote crop productivity; however, these land management systems also allow an efficient pathway for the transport of elements from soils to surface water resources. The nitrate and macro-element compositions of tile-drain effluents from a 40 ha controlled subsurface drainage irrigation system are described and compared to soil nitrate availability. Soil nitrate concentrations reflect soil nitrogen fertilization practices and are sufficiently abundant to promote their transport from the soil resource to the tile-drain effluent waters. The data indicates that: (1) the transport of nitrate-N in tile-drain effluent waters is appreciable; (2) soil denitrification pathways do not effectively reduce soil nitrate-N, even when the controlled drainage system establishes winter-early spring anoxic soil conditions, and (3) the best strategy for reducing nitrate-N concentrations in tile-drain effluent waters in adjusting N fertilization rates and timing of application.

Key Words: nitrate, tile drainage water, denitrification, nitrogen leaching