When you or your agronomist sends soil samples to a laboratory, they measure all the bases—include K, Ca, Mg and Na. And not only do they report the extractable levels they also calculate the base saturation (B.S.,) which compares the amounts of each to the others as a percent. The only base missing is hydrogen (H), which if included would total near 100 percent.
There are a few competing philosophies concerning soil chemistry and interpreting soil test values. These include the buildup and maintenance philosophy, the sufficiency philosophy and the base saturation philosophy. Over the years, an almost fanatical line has been drawn suggesting that a farmer must exclusively use only one of these methods. In my experience, I have found that all three methods have their pros and cons, but none of them is inherently wrong. Among the three, the base saturation method may be the most misunderstood.
One rule to be understood in soil science, or agronomy for that matter, is that you can virtually never say never. Even in making that statement, I have a difficult time saying never. If you hear someone say “never” concerning agronomy, you should probably beware. This is important to keep in mind when considering the base saturation method.
What is the base saturation method?
The base saturation method involves maintaining a certain percentage of cations in the soil to give it “balance.” It’s like the idea that our bodies need a balanced diet to be healthy. William Albrecht, Ph.D., originally developed and promoted this concept back in the mid 1900s at the University of Missouri.
The problem is that some people have instituted what I call “the never factor.” Some feel that Albrecht’s approach assumes that there is a “perfect” nutrient balance in the soil that applies globally and that soils must have this perfect balance to be healthy and productive.
I don’t believe Albrecht meant that at all. His work was primarily completed on soils in Missouri. So, for that part of Missouri, the balance he recommended is possibly the best. However, that doesn’t mean that balance will work in all parts of the world.
How should base saturation be used to enhance soil health?
With all of that said, how is base saturation used to improve soil? That depends on a few factors. Base saturations show the concentration of cations on the soil colloid. It’s important to ask how complete these numbers are. If the tests include sodium and other bases along with calcium, magnesium and potassium, these numbers will be added to calcium and magnesium numbers, falsely elevating them. This may not make a significant difference however, unless sodium levels are high in your part of the world.
In the grand scheme of things, the combination of cation exchange capacity, pH and base saturations will tell a story in most cases. The saturation levels will tell why the soil pH is what it is; it all goes hand in hand. Exchange capacity is a major driver in determining how correct base saturations should be determined. However, low exchange capacity may prohibit use of base saturation percentages.
Nonetheless, base saturations can be used as another piece of the puzzle to determine what actions you must take to improve your soil