The availability of water to plants may be so critically low due to salinity that, lacking proper management, crop production is reduced to the level where the land is abandoned for agricultural use. Arid and semi-arid irrigated soils, in particular, require special attention if saline conditions are to be avoided. Drainage is the most important factor in salinity control, and minimum tillage, by reducing soil compaction and encouraging free water movement, can be a valuable aid.