This is a 5-part series (previous parts at https://croptechcafe.org) on the basic cation saturation ratio (BCSR) concept. Summary of Part 1 & 2 is that authors Bear, Graham, and Albrecht of the BCSR concept in the 1940s-1970s suggested narrow basic cation saturation ratios existed, and a balanced cation saturation of the soil’s cation exchange capacity were needed, or plant growth will be reduced. The first major flaw identified by soil fertility researchers over the past 50 years in the concept is the confounding factor and correlation of base saturation, H saturation, and soil pH. The second major flaw is that the same crop yield and quality can be achieved across a much wider set of basic cation saturation and ratios. Part 3 summarized results from two research studies conducted in Nebraska in the 1970s and 1980s supporting the current scientific consensus that the concept does not hold up.
There are two frequently referenced scientific literature reviews on the BCSR concept. The first was published in 2007 by Kopittke and Menzies entitled “A Review of the Use of the Basic Cation Saturation Ratio and the Ideal Soil” in the Soil Science Society of America Journal (link to abstract). A review and analysis of 52 published scientific papers including the original work of Bear, Graham, and Albrecht led Kopittke and Menzies to state that the ratios of calcium, magnesium, and potassium commonly found in soils do not influence the chemical, physical, and biological fertility of the soil resulting in plant yield difference. The current research data from the 1940s through 2005 did not support the claims of the BCSR concept.
A second literature review was published in 2017 by Chaganti and Culman from The Ohio State University entitled “Historical Perspective of Soil Balancing Theory and Identifying Knowledge Gaps: A Review” in the Crop, Forages, and Turfgrass Management Journal (link to abstract). A review and analysis of 47 published scientific papers including the previous 2007 review was undertaken. Chaganti and Culman again concluded that the BCSR is a theory with no substantial scientific evidence that an ideal ratio of cations is needed to maximize crop yield. However, the reviewers did highlight that further research may still be needed to understand the potential merits and limitations of BSCR concept around crop pest and disease management. Yes, we continue to need new scientific research to learn more.
I know that old habits are tough to break since some private soil-testing labs and crop consultants still use this old and largely disproven BSCR approach. In two weeks, I will share my professional recommendations related to the BCRS concept and some alternative approaches to focus on including new research from Iowa State University on potassium. For inquiries about this and other agronomic resources and programs from Nebraska Extension, contact me at or 402-821-1722. Know your crop, know your tech, know your bottom line at croptechcafe.org
