Thomas, Richard & El Dessougi, Hanadi & Tubeileh, Ashraf. (2006). Soil System Management Under Arid and Semi-Arid Conditions. 10.1201/9781420017113.ch4.
Soil fertility in systems under arid and semi-arid conditions, hereafter referred to as dry areas or drylands, is constrained by environmental extremes of hot and cold temperatures, as well as by low water availability. With some exceptions, these soils have inherently low fertility, low availability of nitrogen and phosphorus, low water-holding capacity, high pH, low soil organic matter (ranging from 0.1 to 3%), shallowness, stoniness, and other speciﬁc problems (Matar et al., 1992). These areas are quite widespread, occupying around 30–40% of the world’s terrestrial surface. Given the vulnerability of these lands to degradation, it is estimated that some 44 million km 2 — 34% of the total world’s area, supporting 2.6 billion people — is at risk from desertiﬁcation (Eswaran et al., 2001). Hence, these lands are of great global signiﬁcance even if their agricultural production potential is relatively low.