Irrigation salinity scenario. A long term simulation on Mediterranean conditions.

In large cropped areas of Southern Italy the use of brackish water for irrigation is quite usual. For this reason, it is very important to verify the suitability of such irrigation waters and the probably long-term damages resulting both on crops and soil. The most simple and effective way to contrast soil salinization is natural salt leaching achieved by rains. The aim of the paper is to evaluate the rain capacity to leach the salts out of the active soil depth on a long-term period. The analysis has been carried out with the use of the physically based SWAP simulation model. A two-year wheat-tomato crop sequence was established and continuously performed in a fifty-year period, from 1951 to 2000. Wheat was always considered a rain-fed crop while tomato was irrigated with water at three different salinity level: 3, 5 and 8 dS m-1 (S1, S2 and S3, respectively). Two leaching periods were identified along the two-year crop sequence: from August 20th to April 20th of the following year (LP1); from April 20th of the same year to April 20th of the following year (LP2). Total salt accumulation periodically reached its maximum value at the time of tomato harvest (August 20th), soon after the irrigated cropping season; conversely, the lower salt accumulation was always attained at the time of tomato transplanting (April 20th), after a comprehensive two-year leaching period. On average, for the whole fifty-year simulation period, the maximum salt accumulation was corresponding to an electrical conductivity of the soil water extract (ECe) approximately equal to 4.9, 6.8 and 8.7 dS m-1, for S1, S2 and S3, respectively. In conclusion, autumn-winter rains still assure the sustainability with respect to soil salinization, but its worsening is dependent by the continuous raise in the salt content of the irrigation water.