Please check the useful PDF attachments for insight

Thank you very much Arvind! This is helpful

For total K you can use 'flame emission spectrometry' at 766 nm.

When soluble form of K is added to soil, a part of it readily converted to less or difficultly available form, which become available later. This fixation of K largely depends on the amount and type of dominant clay  mineral, wetting and drying conditions of soil, presence of other cations, available and added K contents, pH, soil texture and moisture content of the soil. Alternate wetting and drying cycles have been reported to increase the fixation of K, because of expansion and contraction of the mineral colloids, entrapping K ions. Therefore to estimate the K fixation for course textured soils (sandy and sandy loam) are different from fine textured soils (loam to clay). You may use neutral N ammonium acetate solution to measure the fixed K and Flame Emission Spectroscopy (766nm) to measure the total K. The calculation for fixed K is given below:

Amount of ammonium acetate extractable K in untreated soil = A

Amount of ammonium acetate extractable K in treated soil = B

Amount of recovered K ( out of the added K) = B-A

Amount of K added = C

Amount of K fixed = C - (B-A)

K fixation (%) = C - ( B - A) /C x100

Well explained by Dr J C Tarafdar............

Interesting discussion..please find some publications ..might be helpful...

well explained by Dr J.C.Tarafdar  and the publications  of A.kumar  Srivastava excelent 

These all answers helpful me also. Mainly Drs.AK Srivastava & JC Tarafdar Sir,