Nitrate responses in groundwater under grassland dairy agriculture

Abstract

A considerable body of research already exists on establishing nitrate dynamics in agricultural systems' subsoils. However, the capacity to predict rates of nitrogen arrival at the receiving environment, namely surface or groundwaters, has been elusive in an Irish context. A farm- scale hydrogeological investigation was established on an intensive dairy farm, in north Cork, characterised by a freely draining limestone till which forms the subsoil overlying a karstified- limestone bedrock aquifer. The overburden depth is 2.5m, on average, but undulates in depth from 0-4.5m, consistent with the karst terrain. Part of the farm is located within a source protection zone delineated for a public supply borehole located 1.5km to the northeast, in the direction of groundwater flow. This public supply borehole has demonstrated an upward trend in nitrate-nitrogen concentration over the last twenty years, with periodic breaches of the EU MAC, (EC, 1998) of 11.3 mg/l NO3-N, in the last decade. Definition of groundwater-nitrate responses was the fundamental aim of the project, with objectives of measurement of the response of the groundwater system to loadings, both meteorological and agronomic, at the farm-scale.