[Nitrate accumulation and leaching in a Mediterranean horticultural soil].

The town of Hyères (South of France) pumps its drinking water from alluvial ground-water. The influence of the surrounding horticultural activities on the nitrate-nitrogen content of this water has been assessed. 50 ha were studied, 25 cultivated with artichokes, 15 with various seasonal horticultural crops, and 10 with vine, peach-tree and alfalfa. The soil is silty, calcareous and deeper than 3,5 m. From June to December 1979 the nitrate-nitrogen distribution in the first 2 meters of soil was measured in 100 locations. Results show that NO3-N may be found in a great excess under intensive cropping, especially artichokes and peach trees, and so nitrogen leaching may be quite important if the water drains down into the subsoil. Nevertheless cutting off nitrogen losses from the 50 ha projected area would have only negligible consequences on the average quality of pumped water. That is why an help for the agricultural development organisations to promote more efficient use of fertilization over the whole watershed is prefered to very restrictive rules localized in a small area.