Soil and fertilizer phosphorus in relation to crop nutrition

Phosphorus (P) plays a pivotal role in the nutrition of all plants as an essential element participating in a wide array of physiological and biochemical processes occurring in all living organisms (Vance et al. 2003). Historically, of all the nutrients required by plants, P was frequently the one that most limited growth; until P deficiency was corrected many crops did not respond to nitrogen (N), and this is still the case for many soils worldwide. Most crops grown for human food, animal feed, fiber and now for biofuels contain between 0.2% and 0.5% P in their dry matter when sufficient P is available in the soil (Sanchez 2007). In intensive agriculture much of this P can be applied in inorganic P fertilizers and organic manures. Inorganic P fertilizers were first available some 160 years ago after JB Lawes, of Rothamsted (UK), patented a commercially successful method of producing superphosphate, containing water-soluble monocalcium phosphate, from phosphate rock (PR). From the mid 19th century, superphosphate quickly proved to be effective in providing plant-available P on almost all soil types in the UK (Johnston 1994) and has since been used worldwide for this purpose. With the opportunity to use inorganic P fertilizers and organic manures to minimize the risk of soil P deficiency limiting crop growth, there exists the possibility of increasing crop yields to improve food security for an increasing world population. However, the global distribution of PR, the consumption of inorganic P fertilizers and the distribution of P-deficient soils are all poorly matched. Currently, over 70% of the PR reserves that are economically exploitable are located in three countries: the USA, Morocco and Western Sahara, and South Africa (Heffer et al. 2006). The production of PR reached 171 million tonnes (Mt) in 2005, the main producers being USA (24%), China (20%) and Morocco (19%). About 85% of this production was processed for use in agriculture (80% as fertilizer and 5% as animal feed supplement), whilst 15% was used for industrial products, such as detergents (12%; Heffer et al. 2006). In 2005/2006, the annual consumption of P fertilizer was estimated to be 36.8 Mt P 2 O 5 of which 74% was consumed in four regions: East Asia, South Asia, Latin America and North America. Almost 32% was consumed in China and Vietnam, which the International Fertilizer Industry Association’s regional classification includes in East Asia (Heffer et al. 2006).