Nitrate leaching in important crops of the Valencian Community region (Spain).

In the Valencian Community there are many areas in which the nitrate content of groundwater is higher than the limit of 50 mg l(-1) established by the European Union. A recent survey of drinking water quality showed that around 8% of the Valencian Community population had water supplies with nitrate content above that limit. The Valencian Community has an intensive agricultural base that includes citrus trees, fruit trees, and vegetables. A summary of the available nitrate leaching results in vegetable fields and citrus orchards is presented. It is demonstrated in the main vegetables grown, that N inputs were much higher than the values recommended by some researchers, and that nitrate leaching values were in most cases within the range of 150-300 kg N ha(-1). Artichoke, early potato, and onion were the three crops with higher leaching rates than other crops, based on simulation studies made for several of the main vegetable growing areas of the Valencian Community. The mineral N content in the 0-60 cm layer at planting time in the vegetable fields is, in many cases, greater than 200 kg ha(-1); fertilizer application could be greatly reduced if some recommendation system similar to the N(min) system used in other European countries was adopted. A simplified N balance in onion and early potato crops showed that the lower limit for mineralization in the 0-60 cm soil layer during the crop period varied from 65 to 130 kg N ha(-1). In these two crops nitrate leaching varied from 240 to 340 kg N ha(-1), depending on the N fertilizer treatment, and representing about 66-70% of total N input in the onion crop, and from 38 to 65% in the potato crop. Nitrate leaching losses in citrus orchards were, in general, lower than 100 kg N ha(-1) year(-1), representing about 33% of the total N input. A comparison of these results with those obtained in other studies is made. Finally, prospects for improvements in the fertilizer practice of vegetable crops and citrus orchards in the Valencian Community are discussed.