Sources of nitrate leached to groundwater in grasslands of Fermoy, Co. Cork

Abstract

Groundwater contamination with nitrate from agriculture in Ireland has mainly been attributed to specific point sources such as farmyards or to arable farming in certain areas of the country. The current study aimed to investigate the cause of high groundwater nitrate concentrations beneath an intensive dairy farm and to quantify the amount of nitrogen leaching through the unsaturated soil and Quaternary deposits. The study farm was located on a free draining sandstone soil which overlied a limestone bedrock aquifer. The results from the study farm were extrapolated to a regional level to determine if high groundwater nitrate concentrations might be expected in other areas with similar agricultural and geological/hydrogeological properties. A detailed nitrogen budget for the dairy farm was calculated which examined numerous nitrogen sources on the farm. On a plot by plot basis extremely high rates of nitrogen application/recycling could be observed up to 805 kg N per hectare. Annual soil organic nitrogen mineralisation was equivalent to the inorganic fertiliser nitrogen input on the farm, varying from 158 to 346 kg N per hectare.