Geoscience Reference
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Fig. 11.5 Models of tetrahedral or quasi-tetrahedral arrangements of P, O, and eventual H in four
forms of phosphates
Since the end of the nineteenth century when the great importance of phosphorus
was recognized, its defi ciency has been compensated by timely applications of
industrial fertilizers. Rough estimates report that 30-50 % of crop yields are attrib-
uted to natural or synthetic commercial fertilizer. However, excessive applications
of phosphorus fertilizers can exacerbate iron and zinc defi ciencies and increase soil
salinity.
Hence, soil salinization and iron chlorosis could also be the consequences of
overfertilization of phosphate. In addition to these undesirable effects, phosphate
can be fl ushed away by rainwater during soil erosion, especially when excessive
amounts of phosphate fertilizers are applied. The surface runoff erodes and carries
away soil particles fi lled with an abundance of phosphate that readily accumulates
in waters of creeks, rivers, and lakes. When an extreme accumulation of phosphate
occurs in waters of rivers and lakes in combination with an excess of nitrates, we
speak of eutrophication (from Greek eutrophos meaning well nutrifi ed) or hypertro-
phication (from Greek hyper meaning excess or over and trophe meaning nourish-
ment). In other words, the growth and decay of algae and plankton dominate the
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