Material and Methods
Characteristics of the study area
The study was carried out on agricultural soils under vegetable crops of the Segura River valley in the South of Alicante province, Southeast Spain (Fig. 1). These soils occupy a discontinuous area across the fertile Segura River valley, which crosses the centre of the lower Segura region. The Segura River does not have any tributaries in the region and its waters irrigate land of the Segura River valley and part of the lower Vinalopó River valley. At Orihuela, the main city of the study area,the mean annual rainfall is 300 mm and mean annual temperature is 18ºC (Pérez-Cueva, 1994). This annual rainfall is insuff icient for agricultural production
because of the high evapotranspiration rate and the water loss by infiltration. Irrigation is therefore critical to ensure productivity in the region (Bru, 1993).