Leaching of N compounds from swards used for dairying that are N based and irrigated with dirty water/slurry.

Abstract

A study was carried out to investigate nitrate leaching on a dairy farm in Co. Cork. The farm had a history of high nitrate-N in borehole waters and the study aimed to elucidate the causative factors for this. Physical and chemical data regarding the soils, the hydrology, and the N input/output balances were determined and collated. Results showed that nitrate-N concentrations > the EU maximum allowable concentration (MAC) of 11.3 mg/l for drinking water occurred in soil drainage from the light textured soils studied due to a large imbalance between N inputs and outputs. High fertiliser N usage, animal manure and dirty water applications, atmospheric N depositions and soil organic N mineralisation in combination produced these results . While it is recognised that nitrate leaching will vary in amount from year to year the lessons from the study are clear - light textured soils that are used for intensive dairying and which receive high inputs of N are prone to release drainage water high in nitrate.