Managing salinity associated with irrigation at Orange-Riet and Vaalharts irrigation schemes.

Salinity associated with irrigation has in the past, and continues to be arguably the most important factor threatening agricultural production under irrigation. Unfortunately the problem extends beyond the confines of irrigated fields, degrading water resources and resulting in extensive areas of land becoming waterlogged and saline. Poor planning and ineffective water and salt management practices by farmers and managers of irrigation schemes therefore strongly affect the sustainability of irrigation. Researchers are in agreement about the fact that sustainable irrigation is technically possible with the proper design and operation of irrigation and drainage systems, together with the implementation of suitable crop and soil management practices, provided that acceptable political and social structures are in place. The general opinion is that irrigated agriculture will not only survive, but will indeed thrive under realistic circumstances and appropriate management practices. With regard to political and social structures, management practices should however be scientifically sound. South Africa is therefore divided into 19 Catchment-based Water Management Areas (CWMAs). Each of these areas has an agency which manages water resources, co-ordinates water-related activities of water users and other water management institutions within demarcated areas of jurisdiction. Within these CWMAs the water required for irrigation is managed by Water User Associations (WUAs). The WUAs manage the day-to-day supply of irrigation water to the farms and are therefore responsible for the maintenance of water conveyance infrastructure, which includes the removal of drainage water. The next level for water management is on-farm where the farmer has the sole authority over the fate of irrigation water. If the farm is large enough, it may comprise more than one irrigation field, which is the smallest unit where irrigation management decisions are made. The area covered by the irrigation system together with the depth of the potential root zone, defines the physical dimensions of this management unit. The potential root zone of field crops can be up to 2000 mm. Thus an in-field drainage system will be part of the smallest management unit if installed within this depth, which is often the case.