In order to determine the effect of different irrigated crop rotation (1. corn, 2. intensive olive grove (300-400 trees/ha), 3. Corn - barley/oat/wheat (1 or 2 years) sugar beet and 4. Tomato - barley/oat/wheat (1 or 2 years) - Beet) on the organic matter content, pH, electrical conductivity and soil sodicity, we collect and georeferenced 6280 samples from the surface layer of soils (0-20 cm) in the Caia Irrigation Perimeter (located in Elvas and Campo Maior Counties, Portalegre District, Portugal) occupied with those rotations. These samples were mixed in groups of 10, resulting 1 sample, corresponding to an area of 11.1 ha, the one was sent to the laboratory where we proceeded to examine the above parameters. With the use of appropriate software (Geographic Information Systems - GIS), it was possible to correlate these individual soil samples with crop rotations and with the group of soil present (Fluvisols, Luvisols and Calcisols). We found that the use of the abovementioned crop rotations, over about two decades, led to significant differences in soil characteristics, although not always significant from a statistical point of view. The crop rotations using larger water and fertilizers amounts in irrigated crop systems are the ones causing a more evident decrease in soil organic matter and pH and, at the same time, leading to an increase in soil electrical conductivity and exchangeable sodium content.
