The benefits derived of irrigation of agricultural lands may not be sustainable due to the development of salt-affected soils, saline or sodic, with a partial or complete loss of the soil productive capacity. Additionally, there is an increasing contribution of drainage waters from irrigated lands to contamination of soils and waters by salts, nitrates, and other pollutants coming from organic and inorganic products used in irrigated fields. The addition of irrigation water, together with salts, wastes and other pollutants to the soil, may cause drastic changes in the regime and balance of water and solutes in the soil profile. Modelling may be useful to predict those changes, and therefore to guide the selection of practices and systems of drainage and irrigation for a maximum efficiency in the use of irrigation water, reducing the possibilities of losses and contamination of surface and ground waters, and preventing at the same time the processes of soil salinization and sodification. Those models must integrate parameters of climate, crops, soils, fertilization, quality of irrigation water, and of irrigation and drainage management. In the last decades there have been developed several indices and models for evaluation of the quality of irrigation waters and for predicting soil salinization. Many of them are based on the calculation of the leaching fraction requirement, using more or less empirical criteria, which does not allow an application to different conditions to the ones where they were developed. Others require input parameters that are difficult to measure or estimate under field conditions. Here there is proposed a new modelling approach (SALSODIMAR) applicable to very variable and changing conditions, using input parameters easily measured or estimated, which has been developed as a product of successive approximations, based on experiences and validations in very different agro-ecological conditions. The model is based on an independent balance of salts and ions until reaching equilibrium, taking into consideration the effects on soil salinization and sodification of the interactions among irrigation water composition, evapotranspiration, precipitation-dissolution and cation exchange reactions, soil hydrological properties and effective leaching fraction. It may be used to calculate the irrigation and drainage requirements in order to control the salinity and sodicity levels in soils and drainage effluents, in relation to requirements and disponibility of irrigation water, for specific crops and climates. This enables to deduce alternative irrigation and drainage management practices for salinity and sodicity control, under changing physical, social and economic conditions, and with the increasing concern about environmental issues and direct competition of water of good quality for urban areas, industries, recreation, etc. The present version of the model runs in a simple computer Excel program, with immediate response to changes on the given input conditions. There are presented examples where the model SALSODIMAR has proved to be more applicable to predict salinization and sodification under variable condirions of soils, climate, irrigation water and management, compared with other presently proposed more empirical approaches.