An integrated approach for sustainable management of irrigated lands susceptible to degradation/desertification
Salinization is closely associated with desertification, which is defined as “land degradation in arid, semi-arid and dry sub-humid areas resulting from climatic variations and human activities”, with the term “land” including soil, water resources, crops and natural vegetation. The results of the project: AN INTEGRATED APPROACH FOR SUSTAINABLE MANAGEMENT OF IRRIGATED LANDS SUSCEPTIBLE TO DEGRADATION/DESERTIFICATION showed that: -Irrigation with saline waters involves a risk of secondary salinization in clay soils irrigated without any drainage system. -The salinity distribution is related to the presence of clay, with greater values concentrated in the Vertisol area. -The LEACHM model, if properly calibrated, provides accurate prediction of the water content and of the electrical conductivity. -Prediction of the hazard of sodification obtained with the LEACHM model is not satisfactory, and needs further investigation and improvement. -The irrigation system may affect soil structure and bypass flow phenomena, as well as the hazard of salinization at the field scale. Irrigation systems such as micro-sprinkler or sprinkler should be avoided when saline water is used for irrigation. -Exchange of solutes occurs at the contact surfaces between the macropores/cracks walls and the incoming solution in concomitance with bypass fluxes. -Alternating low salinity/sodicity water with a high salinity/sodicity solution can be effective for preventing salinization and sodification. -Cracking and bypass flow decrease the hazard of salinization in clay soil, promoting leaching of solutes. The presence of cracks may increase the efficiency of salt-leaching when a solution having a low salinity is alternated to a solution with a higher salinity. -When cracks are present, lower leaching fractions could be necessary to remove salts from the soil profile. In addition, the low hydraulic conductivity in the bottom layers of a soil profile is likely to be counterbalanced by the presence of cracks. -Crop transpiration and yield in presence of cracks are the result of a combined effect of water available and level of salinity, and can be forecast only by models accounting for both the two factors.