Dear Kome Georges Kogge

You have to subtract the soil solution cations from the cations extracted with ammonium acetate because extracted cations includes water soluble and exchangeable cations. 

That all depends..... If the soil contains a lot of soluble ions (ie is saline), then yes you will be measuring soluble and exchangeable cations. One of the standard procedures is to wash excess soluble salts from the soil as a pre-treatment  before the ammonium acetate extraction (this is usually done with an alcohol solution), but you can also measure the "soluble" fraction and subtract this from the result of the ammonium acetate extraction. Follow the link for an excellent overview of measuring CEC and exchangeable cations for different purposes and in different soil types.

Regards

Andrew

http://www.soilscienceaustralia.com.au/images/sampledata/branches_tab/queensland/occasionalpublications/measuring_soil_cation_exchange_capacity_and_exchangeable_cations.pdf

By leaching soils with NH4OAC we get extractable or available Na and K. If we deduct the water soluble Na and K from extractable values then we get exchangeable Na and K.

When we talk about "available forms" it mean exchangeable and water soluble forms. Growing plant could able to access the available form only. Once the nutrients are pulled from solution phase, nutrients present in the exchange phase are readily available to replenish the pulled nutrients and maintains a dynamic equilibrium between exchange and solution phased nutrients.  

If you can lay your hand on "  Practical Environmental Analysis" by Radojevic, M and Bashkin N. V any edition i think it will help alot.

Here the attachment for estimation of all nutrients in soil and plants

Soil available K includes soil solution K and soil exchangeable K. Soil available K is determined or extracted with 1N NH4OAc. If you want to determine the soil exchangeable K you have to subtract the soil solution K from the available K. Soil solution K can be determined with the extraction of 0.01M CaCl2 solution.

For soluble K it is better to determine K in saturated extract of the soil.

"Available" is a term to represent both water soluble + exchangeable. The extraction of OAc wil obtain the available cations, which the closest representation to plant roots.

We can determine Na, K, Ca in soil  as follows :

Na and K use Advice Flame photometer (CEC low) , and Ca use (versinate )  or uses book form link https://www.researchgate.net/file.PostFileLoader.html?id=58ee1251615e27768e57f259&assetKey=AS%3A482285641310214%401491997265392

http://www.soilscienceaustralia.com...pacity_and_exchangeable_cations.pdf

By amonium acetate methods

your extraction solution is neutral 1M NH4OAC(pH=7). So, you are extracting exchangeable basic cations(Ca, Mg, K and Na). For your answer, it is exchangeable Na and K. If you need to analyze available K you can use Morgan solution ( the mixture of sodium acetate and glacial acetic acid, pH=4.8) as the extractant.  

Cheers!!

Dear Sir, 

Since you intend to determine exchangeable cations, you can use the ammonium acetate method. The main principle of this method involves the displacement of exchangeable basic cations (Na+, K+, Ca2+ and also Mg2+) by a 1M ammonium acetate solution buffered at pH 7. According to this method, the NH4+ ions permit the displacement of the various basic cations from the exchange sites of soil, while the CH3COO- ions will replace the various anions.

For further explanations, you can exploit the book below.

Dipak, S. and Abhijit, H. 2005. Physical and Chemical Methods in Soil Analysis. New Age International Limited Publishers. 4835/24, Ansari Road, Daryaganj, New Delhi, India - 110002. 176 p.

Dear Kome Georges Kogge

You have to subtract the soil solution cations from the cations extracted with ammonium acetate because extracted cations includes water soluble and exchangeable cations. 

So far NH4oAC extracted Na, K, Ca, Mg etc are considered plant available ions and by subtracting paste extract cation, we obtain the exchangeable ones as Islam also has narrated..

Dr. Abdul Ghafoor, you rightly mentioned that  NH4oAC extracted Na, K, Ca, Mg etc are considered plant available ions (solution and exchangeable ions).

Thank you Dr. Islam for the remark. That is correct. 

Good discussion by colleagues on estimating exchangeable cations and plant- available cationic nutrients by using 1 N/M  neutral ammonium acetate.Even though the same neutral ammonium acetate extractant is used in estimating the exchangeable and available cations,there is some difference in methods used for the two purposes.While estimating available cationic nutrients a shorter equilibration time 5-10 minutes is used (Schollenberger and Simen 1945 and Knudsen et al.1982).Quick method compared to estimation of exchangeable cations during CEC estimation.Both exchangeable and water soluble K are estimated together and considered as plant- available.In estimating exchangeable cations a longer equilibration time(say 1-2 hours or keeping overnight say 16 hours)) is used.Probly this may be to ensure extraction of almost all the exchangeable cations.Also the watersoluble cations are not normally deducted from NH4OAc extractable cations in normal soils where the water soluble cations concentrations are small.But in saline soils one has to make a seperate estimate of water soluble cations and deducted from the NH4OAc extractable cations to estimate exchangeable cations(also mentioned by Dr.Ghafoor and many other colleagues).In calcareous soils,researchers suggested the use of NH4OAc at pH 8.2 or 8.5(I N/M neutral ammonium acetate extracts more Ca by solubilization of CaCO3 in calcareous soils).NH4OAc extracts slightly higher amount of exchangeable K as it can extract specifically held K from wedge zones of micaecious minerals(illite ).