Contrasting subsurface denitrification characteristics under temperate pasture lands and its implications for nutrient management in agricultural catchments

Subsurface denitrification plays a key role in the reduction or ‘attenuation’ of nitrate contamination of groundwater and surface waters. We investigated subsurface denitrification characteristics at four sites under pastoral farming in the Manawatū River catchment, in the lower North Island, NZ. Laboratory incubations measured denitrification potential in the vadose zone layers. In-situ push-pull tests measured denitrification rates in the shallow groundwaters. Soils and underlying geology influenced variability of subsurface denitrification. Nitrate reduction was greatest in fine textured soils and reducing groundwaters.