ABSTRACT
The risk of desertification and salinisation is high in areas with an excess of evapotranspiration over precipitation, that is, in arid and semi-arid regions. In order to extend agricultural land in such areas provision of water for plants has to be managed very carefully. This can entail installation of expensive irrigation equipment. Similarly, the maintenance of soil fertility in areas with strong leaching can involve purchase of expensive artificial fertilisers, notably involving input of phosphorus. Only one-third of the land area that is potential arable land if irrigated can realistically be irrigated under existing technological conditions. To irrigate even this one-third would involve major costs.
