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Base cation saturation ratio

Record soil samplesBase Cation Saturation Ratio (BCSR) is the more complex and controversial side of CEC.  To calculate the BCSR of your soil, first determine how many cations your soil can hold (the CEC), then measure what percentage of that whole is filled up by hydrogen, calcium, magnesium, potassium, and sodium.

Over the years, various scientists have hypothesized that there's a perfect ratio at which your soil achieves peak health and highest crop yields.  This idea may have begun with William Albrecht in the 1930s, and in its most recent incarnation can be found in Neal Kinsey and Charles Walters' Hands on Agronomy.  In the latter, the authors posit that soil Hands on Agronomycations should exist in the following proportions: 60-70% calcium, 10-20% magnesium, 3-5% potassium, 1% sodium, 10-15% hydrogen, and 2-4% other cations.

Others argue that what BCSR is really measuring is the far simpler concept of pH and that the increased crop yields organic practitioners notice after trying to correct their cation ratios are simply due to liming the soil.  I haven't read enough to decide what I think about this controversial topic, but I'd be curious to hear pros and cons from folks who have read about or practiced BCSR in more depth.

Meanwhile, if you're interested to see how your soil stacks up, you'll need to look on your soil test for the fields "% saturation K", "% saturation Mg", "% saturation Ca", and possibly "% acidity" and "% base saturation."  In most cases, the three first three fields can be added together to get the last field.  Subtract the saturation of potassium, magnesium, and calcium from 100% and you get the percent acidity (which is the percent hydrogen, and will be 0 if your soil has a pH at or above 7.)  Here's the data from my soil samples:

Mule (1) Mule (2) CP3 (3) Back (4) Front (5) Mom front Mom back
% Sat. K 4.7 3.8 7.1 3.7 6.1 4.5 3
% Sat. Mg 16.7 17.2 13.8 17.6 16.4 13.3 8.5
% Sat. Ca 78.8 79.2 64.8 78.8 77.7 82.3 88.7
% Base Sat. 100.2 100.2 85.7 100.1 100.2 100.1 100.2
% Sat. H
−0.2 −0.2 14.3 −0.1 −0.2 −0.1 −0.2
pH 7.5 7.6 6 7.3 7.4 7 7.3

I'll write about pH tomorrow, but I included the value in my chart so you could see the obvious --- the only acidic soil (my chicken pasture, highlighted in yellow) is also the only one with a percent base saturation less than 100.  More relevantly, notice that all of the samples have more calcium than magnesium.  This relationship, plus the very high values of all of the cations (shown below) suggests to me that I don't need to worry about my Base Cation Saturation Ratios.

Mule (1) Mule (2) CP3 (3) Back (4) Front (5) Mom front Mom back
K (ppm) 825 724 351 615 875 415 351
K Very high Very high Very high Very high Very high Very high Very high
Ca (ppm) 7206 7905 1643 6801 5772 3906 5480
Ca Very high Very high Very high Very high Very high Very high Very high
Mg (ppm) 930 1048 213 926 743 385 320
Mg Very high Very high Very high Very high Very high Very high Very high

What would I do if my BCSR seemed to be out of whack?  The first step would be to correct any CEC problems, then I could add mineral sources of the cations that seemed too low.  However, it's essential to be aware of how supplements will impact your soil pH before embarking on any cation improvement project.

Our homemade chicken waterer kit now comes with instructions for making your own heated waterer.

This post is part of our Holistic Soil Test Analysis lunchtime series.  Read all of the entries:

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This is interesting to read and compare to my soil test.
My best garden sample last year seems in line with your worst! Our garden however was also 1 year old at that point though.
We ammended after the tests, maybe I should get another test to see how much we were able to improve this over the past year.
Our soil was very acidic ranging from 5.4 to 6.7. Looking forward to the rest of the weeks posts.

Comment by Brian Wed Nov 9 16:07:12 2011
I didn't get such an intense test when we first checked soil quality before beginning gardening, but I suspect it was a lot like our chicken pasture. You should think of that similarity as good news --- five years of adding lots of organic matter and your soil will be just as good or better than ours!
Comment by anna Wed Nov 9 17:16:02 2011

One very unique homestead, $1,500 per acre, the opportunity of a lifetime