Irrigation with saline water: benefits and environmental impact

The shortage of water resources of good quality is becoming an important is sue in the arid and semi-arid zones. For this reason the availability of wa ter resources of marginal quality such as drainage water, saline groundwate r and treated wastewater has become an important consideration. Nevertheles s, the use of these waters in irrigated lands requires the control of soil salinity by means of leaching and drainage of excess water and salt. Howeve r, the leaching of salts, soil microelements and agro-chemicals can lower t he quality of the drainage water in the irrigation scheme. The irrigation r eturn flows with water or poor quality are a source of pollution of the sur face water bodies situated downstream of the drainage outlet. Deep percolat ion could also contaminate the groundwater. Therefore, irrigation with sali ne water requires a comprehensive analysis even beyond the area where water is applied. The problem should be treated beyond the scope of the irrigati on scheme, taking into consideration the groundwater and downstream surface water resources of the river basin. Consequently, the sustainable use of s aline water in irrigated agriculture requires the control of soil salinity at the field level, a decrease in the amount of drainage water, and the dis posal of the irrigation return flows in such a way that minimizes the side effects on the quality of downstream water resources. This paper describes the guidelines for a preliminary evaluation of the suitability of water for irrigation and the key factors for salinity control in lands irrigated wit h saline water. Options to improve the quality of the drainage water, strat egies for the reuse of this water and alternatives for disposal of the outf low are also analysed. The final goal is to obtain sustainable agriculture and maintain the quality of the water resources in the river basin. (C) 199 9 Elsevier Science B.V. All rights reserved.