NITRATE LEACHING THROUGH OXISOLS OF THE LOYALTY ISLANDS (NEW-CALEDONIA) UNDER INTENSIFIED AGRICULTURAL PRACTICES

For the uplifted coral atolls of the Loyalty Islands (New Caledonia), the prime source of potable water is the freshwater lenses that underl ie the islands. The recent adoption of more-intensive agricultural pra ctices, particularly the use of nitrogeneous fertilizers, may, however , represent a threat for these fragile Pacific ecosystems. To assess t he risk posed by nitrate leaching, experiments have been conducted on the permeable oxisols of the island of Mare, using both cropped and ba re soil sites. Drainage below the root zone was found to be very impor tant, about 50% of the rainfall, even on the cropped site. The soils a re thin and permeable, and the frequent tropical storms have high rain fall intensities. Nitrate fertilizers thus have potential to be leache d, in large amounts, even up to 100% of the nitrate supply, especially if fertilizers are not supplied according to weather conditions and i n concert with the plant's ability to extract them. (C) 1998 Elsevier Science B.V. All rights reserved.