2.2 Phosphorus Contents and Forms
2.2.1 Total Phosphorus
The total phosphorus content of the soil is of no direct practical importance, but it had often
been used as a weathering insides Total phosphorus in the top soil decreases with
increasing intensity. Olsen and Englestad (1972) stated that representatives soil from the
United States south east about 500 ppm, and tropical soils about 200ppm. Because of
thegreater are extent of highly weathered soils in the tropics. This is generally true, but it
ignores the sharp differences among tropical soils.
Dot Clea
2.2.2 Organic Phosphorus
In mineral soils, the organic fraction generally constitutes 20 to 80% of the total phosphorus
in surface soil horizons. The deeper horizons may hold large amounts of inorganic
phosphorus, especially in soils from arid and semi arid regions (Brady and Weil, 2012). The
organic form is found in humus and other organic materials (Schulte and Kelling, 1996).
Phosphorus in organic pools indicates long-term sequestration potential under flooded
conditions, but may be unstable under drained conditions due to soilOxidation and organic P
mineralization (Sanchez and Porter, 1994) Decomposition of organic P, as found in humic
and fulvic acids, and lignin-containing residual fractions, depends on heterotrophic microbial
activity, thus these pools are more stable under flooded conditions since decomposition rates
are lower in the absence of O₂ (Wright and Reddy 2008)
Earlier reports by Agboola and Ayodele (1983) and Akinrinde and Obigbesan (2000)
showed organic P is a significant determinant of P availability in tropical soils
2.2.3 Inorganic Phosphorus Fraction
In spite of the large attention that phosphorus has received over decades of intensive research
in the 20th century, because of the lack of appropriate methods for studying its speciation and.