Mr.Long,the following publication gives a fair account of available P estimation,methods used and the interpretation of data.
Understanding soil tests for plant-available phosphorus.Maurice Watson and Robert Mullen 2007 Available online.
ohioline.osu.edu/agf-fact/pdf/Soil_Tests.pdf
Mr.Long,You may also consult the following conference paper.Soil phosphorus testing for crop production and environmental purposes. by Antonio Mallarino
www.agronext.iastate.edu/soilfertility/info/ICM_1999_Pbio&Testing_Publ.pdf
Thanks so much Mr. Annangi Subba Rao, may you define the phosphorus adsorption capacity of soil?
Soils have high reactive surfaces containing Fe,Al,Ca etc.which can adsorb the phosphate ion.I have earlier provided a reference of Olsen and Watanabe( 1957) in another question asked by you.That paper gives you lot information.The Langmuir adsorption equation contains two constants which can describe the adsorption maximum and the bonding energy.of adsorption.In the Langmuir adsorption study,the c/x/m is plotted against c in a linear form.
c/(x/m)=1/Kb+c/b
Where c is the equilibrium P concentration;x/m is amount of P adsorbed per unit weight of soil;K is a constant related to the bonding energy ;b is adsorption maximum .From the slope 1/b and the y intercept 1/Kb both b and K can be calculated.
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