ABSTRACT
Soil infertility is a primary constraint to plant productivity over the majority of the Earth’s land surface. Nitrogen is often limiting in young soils of the temperate zone, whereas phosphorus (P) is a primary limitation in most forests, weathered soils
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and the humid tropics, which support the majority of terrestrial plant biomass (Figure 8.1) [1,2]. Low soil phosphorus availability is caused by several factors, including the reactivity of orthophosphate with common soil constituents such as Fe and Al oxides, resulting in compounds of limited bioavailability, especially as soil weathering progresses, and the fact that the phosphorus cycle is open-ended and tends toward depletion.
