A simple indicator for diagnosing nitrate leaching risk below the root zone using the Tensionic tensiometers

Soil water potential and nitrate content in soil solution were measured sim ultaneously, using Tensionic tensiometers, in farmers' fields at three diff erent sites for assessing nitrate leaching. The above measurements were mad e every 10 days at two depths below the rooting zone, for three different c ropping systems; namely, grassland, field crops, vineyard in 1994 and 1995, and under field-grown and greenhouse-grown salads during the winter 1996-1 997. A nitrate leaching risk indicator was calculated by using the soil wat er potential gradient and the nitrate concentration of the soil solution be low the rooting zone. This approach can be used to analyse nitrate leaching under different management practices for a range of cropping systems. It w as also possible to diagnose the contribution of groundwater containing a r elatively high level of nitrate to nitrogen and water supply to crops. (C) Inra/Elsevier, Paris.