Potassium is highly soluble in water. It gets solubilized due to many reasons and one of the reason may be due to the presence or absence of different soil biota and due to the extent of soil aggregation. Leaching of K is one of the major factor for deficiency of K.

Currently, little information is available on potassium solubilization by bacteria, their mechanisms of solubilization and effect of KSB inoculation on nutrient availability in soils and growth of different crops. Sheng and Huang found that potassium release from the minerals was affected by pH, oxygen and the bacterial strains used. The efficiency of potassium solubilization by different bacteria was found to vary with the nature of potassium bearing minerals and aerobic conditions. The extent of potassium solubilization by B. edaphicus in the liquid media was more and better growth was observed on illite than feldspar. Therefore, there are immense possibilities for further increasing the production of crops by application of K-bearing rock materials and potassium solubilizing bacteria as biofertilizers.

refer : http://article.sapub.org/10.5923.j.microbiology.20130301.04.html

Different environment factors such as pH,temperature,nutrients,oxygen,agitation, and nature of the rock material affected the rate of pottasium solubilization.

All salt-K are soluble in water, the amount of the salt dissolve per 100 mL of water is determined by the radical/anionic specie e.g. K2SO4 is relatively less soluble than KCl, which goes without saying that temperature that affect solubility will indeed impact on soil K solubilization.

In soil we expect the chemical property of K to be the same, therefore the solubility should also be the same. The extent of solubilization of soil K is determined by concentration of solute K, hence the soil moisture content/status which why in spite of the soil cation exchange capacity, leaching is a cause of concern.

Microbial mediated K solubilization arises form satisfying their requirement for same and their small size and abundance put them at advantage to better mine the soil and it follows that at completion of their life cycle the K and any other nutrient assimilated will become more available.

Soil pH as pinpointed by Dr Sukla and Pradhan will also affect K solubility as it is for any other bases in soil, but more importantly the impact of pH is through competition for exchange sites in soil rather than enhancing the solubility per se. For instance for soil having high pH does not lower leaching of K. There are evidence that through liming, Ca competes for exchange sites, induce K release in soil solution which is in turn more expose to leaching.

Soil texture is another factor affecting K solubility e.g, the 1:1 type compared to the 2:1 type where relative ionic charge density affect retention property. Clays of volcanic ashes (the Short Range Order Type) ionic charge type is also affected by pH switching from cationic sites to ionic sites again K retention is affected and hence solubility.

From soil texture we have also interlayer/lattice trapping or fixing of K ions and in this context the soil K is permanently fixedostly because K is completed isolated/protected from the eroding action of water.

Therefore depending on which mechanism is dominant, potassium fertilization should be formulated accordingly.

Add organic matter to the soil and this will have better K retention and exchange rate

Coupled with the previous answers, I consider the relationship of potassium with other nutrients should affect its availability, but do not know these mechanisms.

As a very high soluble cation K has mainly two limiting factors for its permanence in soil:

- Retention: In this way content & quality of clays is determinant.

- Solubilitation: Amount of water in the system is crucial to the monvement to the plant root or to soil depth.

Of course, SOM can exerts sorption on K, but in less intensity compairing with clays; in addition, remember that ions NH4+ & K+ has the same physic-chemistry behaviour, and clays & even plants can confuse both them.

Furthermore, antagonysm is common in relation with other divalent cations, but this is another subject.

As I know, One of the most important factors limiting potassium solubilisation in the soil is the anion intensity of the soil. More anion intensity in the soil causes more limitation of potassium solubilisation and increases potassium fixation in the soil.

Nutrient audits and statistics of fertilizer use demonstrate that there is a need for K fertiliser production to double to meet the needs of the world’s population at the present day. In these circumstances, the production of conventional K fertilisers derived from potash salts needs to increase, and might be supplemented by novel K fertilisers, particularly in regions distant from sources of conventional products. One possibility is to use K silicate rocks, especially in deeply weathered tropical soils where leaching of readily soluble nutrients is an issue , DAVID MANNING1 , MALLELY SANCHEZ LIMON1,2, KIRSTEN BRANDT3 , MINERALOGICAL CONTROLS ON K FERTILISER FUNCTION , 16 th World Fertilizer Congress of CIEC ,2014,pp132-134.

Most agricultural soils contain large reserves of phosphorus (P), a considerable part of which

accumulates as a consequence of regular applications of P fertilizers. However, a greater part of soil

phosphorus, approximately 95–99% is present in the form of insoluble phosphates and hence cannot

be utilized by the plants. In the present study fungal strains isolated from agriculture soil, having

potential to solubilize insoluble inorganic phosphates were characterized. Two fungal isolates were

tested for their tricalcium phosphate (TCP) solubilization efficiency in both solid and liquid medium.

Isolates were identified as Aspergillus sp. and Penicillium sp. depending upon their colony morphology

and microscopic studies. Phosphate solubilization was related to pH decrease caused by growth of

fungus in medium containing glucose as carbon source. Aspergillus sp. solubilized 480
g/ml of

phosphorus, while Penicillium sp. solubilized 275
g/ml of phosphorus from 0.5% tricalcium phosphate

after 4 and 3 days of growth respectively. Both the strains show diverse levels of phosphate

solubilization activity in liquid broth culture in presence of various carbon and nitrogen sources. Drop

in pH during growth was more prominent in absence of TCP in the liquid medium. This indicates that

absence of soluble P in media induces the acid production. Phosphate solubilizing microorganisms

convert insoluble phosphates into soluble forms generally through the process of acidification,

chelation and exchange reactions. Thus such microorganisms may not only compensate for higher

cost of manufacturing fertilizers in industry but also mobilizes the fertilizers added to soil.African Journal of Biotechnology Vol. 5 (10), pp. 850-854, 16 May 2005