Soil salinization represents a precondition for desertification, defined as "degradation of land in arid, semi-arid and dry sub-humid areas resulting mainly from adverse human impact" (UNEP, 1991). Recent investigations proved that soil salinization and subsequent desertification may be influenced by bypass flow, i.e. the rapid transport of water and solutes via macropores and/or shrinkage-cracks to subsoil and to groundwater. Bypass flow may increase hazard of salinization of subsoil and groundwater, significantly decreasing efficiency of salt-leaching and crop yield.
For a proper prediction of hazard of soil degradation and for a sustainable management of irrigated lands susceptible to degradation/desertification, it is therefore necessary to develop and validate management-oriented models accounting for bypass flow. Analysis of the existing physically-based models that can be used for management of irrigated areas susceptible to land degradation/desertification evidences the lack of models accounting for bypass flow. Development of an approach accounting for bypass flow could be achieved by extending the salinity version of the Leaching estimation and Chemistry model LEACHM with modules describing bypass flow of water and solutes.
Validation of the extended LEACHM and of the original LEACHM performed through comparisons between predicted and measured values of salinity and sodicity collected in a Sicilian and in a Spanish pilot-areas, will make it possible to check the performance of the original and of the improved version and to assess the relevance of bypass flow on salt-accumulation and salt-leaching under field conditions. A sensitivity analysis will make it possible to select the parameters (climatic, physical, chemical, hydrological) more relevant to the process of salinization/desertification, to be used as environmental indicators. Analysis of the results obtained by model application under different possible scenarios will allow threshold values of the selected indicators to be established.
Integration of the selected indicators in conjunction with management scenarios and threshold values in a Geographical Information System (GIS) will allow results obtained on the study-sites to be scaled-up to larger areas where similar conditions can be identified.
This final step could be helpful to select countermeasures and/or guidelines useful to prevent extension of salinization/desertification at different scales and to prepare maps indicating the place and the rate of hazard.
Development of an advanced approach for sustainable management of lands irrigated with saline/sodic waters could lead to reconsideration of previous assessments about suitability of some saline/sodic waters. Application of the validated model could lead to the effective evaluation of hazard of soil quality degradation, grounwater salinization, reduction in crop-yield. Previous statements about water suitability and environmental hazard could be revised using the validated model.
Application of the advanced model could certainly make it possible an improved use of the available water resources by simultaneously minimizing the connected environmental hazard, increasing sustainability.
Funding SchemeCSC - Cost-sharing contracts
6701 AR Wageningen