dear portia, This work done by Bear and co-workers in 1945 identified

optimum saturation levels of the basic cations for an ideal soil at 65% saturation of

Calcium, 10% saturation of magnesium and 5% saturation for Potassium. 

regards

Yes i agree with Shashi Pathania. However, the base saturation will vary with soil to soil. Example in alkaline soil base saturation will be high than acidic soil. In acidic soil Al and H will occupy some of the surface of soil. Hence, it will reduce the base saturation level of the acidic soil. Using Basic Cation Saturation Ratio, one can determine the ideal proportion of the basic cations. However it can not be considered as sufficient approach. Perfect fertilizer recommendation cannot be made using this approach. if the base saturation is low means one can recommend for fertilizer application

Portia,

CEC measurement methods are of 3 basic types. Effective CEC is determined at existing pH by extracting basic cations with unbuffered ammonia chloride and Al extracted with 1 N KCl. CEC at a buffered pH 7 has bases extracted with ammonium acetate and H and Al determined by titration to pH7. CEC at pH 8.2 (known as sum of cations) extracts bases with Barium Chloride and titrates H and Al to pH8.2. The results differ little if the soil is dominated by 2:1 clay (montmorillonite) but differ greatly if the soil clay is Kaolinite or if there is substantial organic carbon present. With regard to a desired base saturation percentage the effective CEC measurement is best related. For most crops such as corn base saturation of the effective CEC needs to be greater than 40%, the higher the better. For Al sensitive crops such as alfalfa base saturation should be greater than 80%. Because the buffered CEC measurements do not consider the ambient pH of the soil it is not possible to evaluate a satisfactory base saturation percentage of a given soil sample.    

Portia,

Sorry I sent the first response before I completed it. In Soil  Taxonomy a base saturation percentage of 50% or more by the pH 7 CEC method is used to define mollic epipedons as more fertile than the more acid umbric epipedons in surface horizons containing 0.6 % or more organic carbon. A base saturation % of 35 or more via the pH 8.2 method is used in essentially organic carbon free sub soil to distinguish more fertile Alfisols from less fertile Ultisols.

Best regards,

Depends on the soil and the conditions. Here in Brazil we were used to define 65-70%. However, today we see that in several situations, for our acid soils 50% is OK

The most common abundant cations in soils are Ca+2, Mg+2, K, Na+ and in strongly acid soils Al+3. It is common practice to measure the concentrations of these most abundant cations. These may be summed to give an approximate value of effective CEC.

Although the desired levels of cations vary based on soil types and pH, the desirable proportions of CEC of Ca, Mg, K, Na and Al are 65-80%, 10-15%, 1-5%, 0-1% and

Fertilizer recommendations based on ideal cation ratios is much debated subject from 1945 classical work of F E Bear and coworkers.However the ratios can vary  in contrasting soils and the view expressed by Getachew Agegnehu  appears to be quite O.K . for many practical purposes. I also appreciate the detailed reply of Stanley .W Buol.Appropriate method of CEC determination and also determination of basic cations and Al,H ions is very important to arrive at  the ratios and recommending lime , K and Mg  application.

agree with Stanley

See text box 2 in the link provided

http://vfrc.org/getdoc/a88fc6c3-27c1-443a-85e2-40eff0450892/VFRC_Report_2015-1.aspx

Interesting discussion..

From the 1920s to the late 1940s, a great and largely un-sung hero of agriculture, Dr. William Albrecht, did a lot of experimenting with different ratios of nutrient cations, the Calcium, Magnesium, Potassium and Sodium mentioned above. He and his associates, working at the University of Missouri Agricultural Experiment Station, came to the conclusion that the strongest, healthiest, and most nutritious crops were grown in a soil where the soil's CEC was saturated to about 65% Calcium, 15% Magnesium, 4% Potassium, and 1% to 5% Sodium. (No, they don't add to 100%; we'll get to that.) This ratio not only provided luxury levels of these nutrients to the crop and to the soil life, but also strongly affected the soil texture and pH.

The percentage of the CEC that a particular cation occupies is also known as the base saturation percentage, or percent of base saturation, so another way of describing Albrecht's ideal ratio is that you want 65% base saturation of Calcium, 15% base saturation of Magnesium etc. Don't get too hung up on these percentages; they are general guidelines and can vary quite a bit depending on soil texture and other factors.

It's still a little-known fact that the Calcium to Magnesium ratio determines how tight or loose a soil is. The more Calcium a soil has, the looser it is; the more Magnesium, the tighter it is, up to a point. Other things being equal, a high Calcium soil will have more Oxygen, drain more freely, and support more aerobic breakdown of organic matter, while a high Magnesium soil will have less Oxygen, tend to drain slowly, and organic matter will break down poorly if at all. In a soil with Magnesium higher than Calcium, organic matter may ferment and produce alcohol and even formaldehyde, both of which are preservatives. If you till up last years corn stalks and they are still shiny and green, you may have a soil with an inverted Calcium/Magnesium ratio. On the other hand, if you get the Calcium level too high, the soil may lose its beneficial granulation and structure and the excessive Calcium will interfere with the availability of other nutrients. If you get them just right for your particular soil, you can drive over the garden and not have a problem with soil compaction....

In Brazil, we use 70% for the soils of southern Brazil and 50% for the Cerrados' soils, and edaphic type of savannah that covers all Central Brazil

The following review article may clarify many things.A reviw of the basic cation saturation ratio and the "ideal"soil.Kopittke,P.M.Menzies,N.W.2007 Soil Sci.Soc.Am.J. 71:259-265.  doi:10.2136/sssaj2006.0186  probably available on researchgate.net