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.

This chapter is divided into seven sections. Following the Introduction we give an up-to-date account of the interactions between soil and fertilizer P in relation to the availability of P to plants. This summarizes the findings of part of a comprehensive review on the efficiency of soil and fertilizer P use commissioned by FAO and four other institutions (Syers et al. 2007). The acquisition of P by the roots of crop plants is then considered in relation to its availability in soil. In the following two sections we discuss first crop nutrition and the efficient use of P where soil P is adequate, and then the acquisition of P by plants where P supply is limited and to the adaptive mechanisms induced in plants by P deficiency and their possible exploitation. In both these sections, which discuss crop production in very different agro-environments, we present some possible ways to increase the efficiency of use of both soil and fertilizer P. In the final two sections we deal briefly with environmental and ecological aspects related to the use of P in crop production.