Base 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 cations 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.

This post is part of our Holistic Soil Test Analysis lunchtime series.  Read all of the entries: Holistic soil test analysis Cation exchange capacity Base cation saturation ratio Soil pH Heavy metals in garden soil

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.



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