The amount of phosphate in untilled soil is normally
quite small and remains fairly stable because it is
present as the insoluble salts of Ca 2+, Fe 3+ and A13+.
To be used by plants, the phosphate must be released
as the soluble H2PO 4 anion, in which form it can be
taken up by plant roots. Although acidic soil
conditions will facilitate phosphate absorption, phosphorus
is the nutrient which is often in shortest supply
for the growing plant. Most mined phosphate is thus
destined for use in fertilizers and this accounts for up
to 75% of phosphate rock in technologically advanced
countries and over 90% in less advanced (more
agriculturally based) countries [1].
Industrial effluents and excessive fertilization of
natural waters due to detergents and untreated sewage