Significance of phosphorus for agriculture and the environment in the West Asia and North Africa region

Fertilizers have been largely responsible for the massive increases in world food production in the past half century that permitted accelerated global population growth to current unprecedented levels. Fertilizer use not only impacts crop yields but also affects animal production. While nitrogen (N) has been the main driver of such changes, phosphorus (P) also has a major role. Like N, the use of P fertilizers can have implications beyond the farmers' fields, if excessive amounts are applied. The past four decades have witnessed overuse of P fertilizers as well as animal manures in the intensive agricultures of some European countries and North America. Yet ironically in many areas of the world, notably Africa, agricultural output is largely constrained by low soil P in combination with little or no P fertilizer application. Rock phosphate is the global source of the raw material for P fertilizer. However, resources are finite, and therefore efficient and wise use is of paramount importance. The vast West Asia and North Africa (WANA) region is one where agricultural output is beset with major environmental constraints. Yet fertilizer use in the region is still in the incipient to early development stage, ironically in view of the fact that major deposits of exploitable rock phosphate are found in the region, mainly in Morocco and Tunisia. With the predominantly calcareous soils of the region being inherently low in available P, the main focus in the past few decades has been on promoting P use and its efficient management in rainfed and irrigated agriculture. In the 1960s and 1970s, virtually no fertilizer was used in the region, with rapid increases in N and to a lesser extent P since then. The sharp transition from low-input traditional agriculture to conventional modern agriculture has particular implications for efficient P fertilizer use from the economic and environmental standpoints. This review seeks to present a broad overview of P in countries of the WANA region, which varies considerably with respect to economic development and the level of agricultural research, education and extension. It presents the background global considerations with respect to P supplies and use, as well the agricultural context for the region, including climate and cropping systems; it draws heavily on research on soils and soil-P chemistry from Spain, which though technically excluded from WANA, has much in common with the Mediterranean region, and highlights P research from Pakistan at the eastern fringes of WANA. It highlights the discrepancy in P use between developed and developing countries such as those of WANA. The review to some extent builds on extensive research carried out in Syria by the International Center for Agricultural Research in the Dry Areas (ICARDA), with secondary emphasis on countries of the region, many of which collaborate closely with ICARDA. The review covers the past three decades, highlighting progress in field trials on fertilizer use with the region's main crops in relation to rainfall, cropping systems, soil test levels, and efforts to identify P-efficient genotypes and enhance soil P fertility with mycorrhizae. Despite the many isolated, uncoordinated, and often-overlapping, and indeed conflicting, research efforts that have taken place in the region, we have attempted to show a gradual progression in knowledge of P in relation to soils and crops. Developments with regard to P, in the overall framework of agricultural research, have contributed to increased output in the WANA region. Much of the documented research has contributed to the global information on soils of arid and semi-arid regions. Despite achievements in applied research, poorly developed technology transfer systems and weak analytical facilities remain as stumbling blocks to the widespread dissemination of the accumulated knowledge on P use to farmers. © 2012 Elsevier Inc