The impact of agriculture on ground water quality in Slovenia: standards and strategy

Ground water and water from springs are sources used for water supply in Slovenia. The quality of these waters has been monitored since 1987. Among 12 main ground water aquifers in Slovenia the amount of nitrate exceeds the allowable level (50 mg/l) for drinking water in areas with more intensive agricultural production with higher concentrations of animals (two livestock unit - LU/ha) and where drainage of sewage water is not excellently arranged or where quality of river water that effluent ground water is not well. The identification of nitrogen surpluses has been done on regional and farm level (using normative approach). This method is taking into account nitrogen input from mineral fertiliser, animal wastes and the deposition from the atmosphere minus nitrogen uptake of harvested crops and ammonia losses to the atmosphere. On an average nitrogen input from mineral fertiliser is low, while input from organic manure is rather high - 90 kg/ha. Average net-balance surplus for Slovenia is about 56 kg N/ha. The differences between regions are relatively high. In the most intensive arable region with high intensity of animal husbandry (2 LU/ha) nitrogen surplus is about 90 kg/ha. This region can be identified as vulnerable for nitrogen leaching into ground water. In regions with limited growing conditions for agriculture plants (climate, soil depth) just small increase of livestock density can cause high nitrogen surpluses. Our Slovenian legislation, which almost entirely corresponds to EC Nitrate Directive and Code of Good Agricultural Practice intends to reduce mineral surpluses in agriculture and meet the standards of nitrate in drinking water. (C) 1999 Elsevier Science B.V. All rights reserved.