The concept of “ideal” soil and soil balancing seems to have started with Oscar Loew’s 1892 “discovery” that too much calcium or magnesium can be a bad thing. After measuring calcium and magnesium in the soils where his plants were growing poorly, Loew concluded that if there’s too much of one and not enough of the other, the plant suffers. In fact, in spite of studies he did with D.W. May showing that test plants grew optimally at a wide range of ratios, Loew decided that plants required the soil to have a ratio of Calcium to Magnesium (Ca:Mg) of 5:4. Was this really so? In fact, subsequent research by others showed that there was no evidence that his ratio improved growth, and that in fact, poor yields were a result of calcium deficiencies.
In spite of the information showing that ratios didn’t impact plant growth, other scientists continued to explore them, motivated by good intentions toward those raising our food. Firman Bear and his coworkers came up with the “ideal soil balance” as a way to reduce potassium uptake by alfalfa which could potentially reduce fertilizer costs for farmers. They focused on the concept of cation saturation, calling it “Base-cation saturation ratio”, or BCSR for short. (You may remember cations as positively charged ions that provide nutrients to plants, but here’s a refresher if you’re feeling fuzzy on the subject.) The ideal balance of cations that Bear and his gang came up with are almost identical to the ratios proposed by William Albrecht, a soil scientist working at the University of Missouri at this same time: Hydrogen, 20% (Albrecht said 10%), Calcium 65% (Albrecht said 60-70%), Magnesium 10% (Albrecht said 10-20%) and Potassium 5% (Albrecht’s was 2-5%). Albrecht also added .5 to 5% for Sodium and 5% for other cations.
So did these ratios work? Actually no. Bear and his colleague, Stephen Toth, did further experiments revealing that so long as calcium was adequate, no specific ratio produced better yields. Other scientists reviewed the literature and undertook studies of their own and agreed with Bear and Toth, finding, nope, this ratio idea is cute, but not at all valid. More recently, field trials in Australia over a 6-year period compared barley, wheat, canola, and lupins grown in a wide range of Ca: Mg ratios. Variations in the ratio from 0.4:1 up to 17:1 didn’t really make a difference.
But in spite of this, the BCSR concept lives on in the work of William Albrecht. He left his papers explaining soil balance and the cation ratios to his friend Charles Walters, who went on to found the magazine Acres USA and promote the heck out of the balanced soil concept. Through the 1960s, 80% of soil tests in the north central US used the BCSR concept to make recommendations, and the Australian turf industry was still relying on soil testing labs using BCSR in 2007. (Note: University soil test labs do not base recommendations on the BCSR concept.)
BCSR Costs and Benefits
What researchers have found is that yields don’t go up, but fertilizer costs do when BCSR is the basis for recommendations. For example, when soil test recommendations are based on the crops’ needs, rather than on BCSR, the test is measuring if there are sufficient quantities of the necessary nutrients in your soil to grow the plant in optimal conditions. The fertilizer recommendations are designed to fill in any shortfalls and are generally about half the cost of trying to get Ca, Mg, and K in “balance” under BCSR. The results of a side-by-side comparison of BCSR and Sufficiency Levels of Available Nutrients (SLAN) showed that BCSR cost $9.27 per acre more and did not improve yields. Researchers concluded that reaching the levels required by BCSR could take years of fertilization, and profits would not increase, even when prices for organic products was factored in.
Of course another part of the equation are the plants themselves. What do they say about soil balancing? As it turns out, plants know what they like, and when researchers tested what they like, the ratios of cations (nutrients) in the plants were pretty constant across a variety of soil types. Plants take up the nutrients they need if the soil holds enough. This shows us that it’s not the ratios in the soils themselves as much as it is having “enough.” And how do you know if you have enough? You check the levels in your soil and add where you’re deficient. It’s a much more cost-effective way to go.
But I think My Soil Balancing Is Working!
Farmers who built up their soils in the name of sustainable agriculture are often using many tools that inherently improve soil (applying compost, planting cover crops, etc.), but attributing their progress to balancing soil.
Researchers that have studied BCSR theories find that they don’t hold up. They have shown that having the “proper” balance of calcium and magnesium does not reduce soil compaction. Soil balancing does not increase microbial activity, because, as researchers found, almost all soil organisms subsist on organic matter, not the minerals being balanced as part of BCSR. Though proponents also list reduced weed growth as a benefit of soil balancing, research has shown no such impact.
When the research in favor of BCSR is evaluated, scientists have concluded that improvements in production can be explained by changes in pH. That’s why your extension agents, and folks from your local NRCS and Conservation District offices recommend liming, which increases the pH. The proper pH is well-known for improving microbial activity, soil structure, nitrogen fixation, and forage palatability. It also can correct calcium and magnesium deficiencies, and increase nutrients available for plant uptake.
The concept of balancing soil cations has been thoroughly reviewed and as happens with science and our understanding of the natural world, this is a concept that has been disproven. The bottom-line is that BCSR is based on information that has been refuted multiple times and in multiple ways. It falls into the realm of unsubstantiated conclusions, and costs practitioners time and money that they could better save or spend elsewhere.