Phosphorus

The soil organic phosphorus (P) fraction may be derived from plant residues and from soil flora and fauna tissue and residues that resist rapid hydrolysis. Phosphorus in soil extracts and plant ash can be determined by instrumentation or by wet chemistry. To understand the inorganic P status and availability in soil, diverse fractionation schemes and soil tests have been developed. Four methods have been used to determine total P in soils: sodium carbonate fusion, perchloric acid digestion, H2SO4 (sulfuric acid)-H2O2-hydrogen fluoride digestion, and sodium hypobromite oxidation followed by dissolution in dilute H2SO4. The total organic P is generally determined by the ignition method, concentrated H2SO4 as a primary extractant. Anion exchange resin in aqueous suspension with soil simulates plant roots by removing the dissolved phosphate from the soil solution via surface adsorption. The P buffering capacity, an inherent soil characteristic, is closely associatd with P diffusion in soil.