Basic Cation Saturation Ratio Concept, Part 2: Field research after the 1970s

As a reminder, this is a 5-part series including the development of the basic cation saturation ratio (BCSR) concept (read at https://croptechcafe.org), field research after development (today), expanded details on field research in Nebraska (Jan. 17), the most recent scientific consensus from two published literature reviews (Feb. 3), and my current recommendations related to the BSCR concept (Feb. 17).

The authors Bear, Graham, and Albrecht of the BSCR concept in the 1940s-1970s suggested that an ideal and narrow basic cation (calcium – Ca, magnesium – Mg, and potassium – K) saturation ratios existed and a balanced cation saturation of the soil’s cation exchange capacity were needed, or plant growth will be reduced. Bear and colleagues recommended basic cation ratios of Ca/Mg at 6.5/1, Ca/K at 13/1, and Mg/K at 2/1. Albrecht suggested the cation saturation percentage of the soil cation exchange sites: 60-75% calcium (Ca), 10-20% magnesium (Mg), 2-5% potassium (K), 10% hydrogen (H), 0.5 to 5% sodium (Na), and 5% other cations. Last time I left you hanging on this question, “do you think the BSCR concept still holds up to the last 50 years of scientific rigor?” The simple answer is no.

The first major flaw identified by soil fertility researchers over the past 50 years in the BSCR concept is the confounding factor and correlation of base saturation, H saturation, and soil pH. We know soil pH impacts nutrient availability, crop growth, and biological nitrogen fixation in legumes. Albrecht wrongly concluded that plants are not sensitive to soil pH and nitrogen fixation is related to soil pH merely as it denotes a calcium supply decrease. We know that a soil pH of 5.8 or above is recommended for soybean nodulation and N fixation. The base saturation will increase as soil acidity (H) is neutralized. Therefore, Albrecht was correct in that the H% saturation should be low and base saturation high because most crops perform well when soils are slightly acidic (soil pH of 6.5 to 6.8). Additionally, we also know that most plants do not thrive, and soil structure is negatively impacted in sodic soils (Na base saturation > 15%). K-State provides a warning back with soil sample results when the exchangeable Na is higher than 10%, so having a low percent of Na saturation suggested by Albrecht was in general sound.

The second major flaw identified by soil fertility researchers over the past 50 years in the BSCR concept is that the same crop yield and quality can be achieved across a much wider set of basic cations ratios (Ca/Mg, Ca/K, and Mg/K). Simply put, the target or ideal ratios determined by Bear, Graham, and Albrecht are much too narrow. For example, 65% Ca and 10% Mg base saturation equals a Ca/Mg of 6.5/1 (Bear). Numerous research studies have found no difference in crop performance across a wider range of Ca/Mg ratios (1/1 – 100/1) in field research and greenhouse pots experiments. Even taking the wider range for a balanced soil with Ca/Mg ratios of 3/1 to 7.5/1 calculated from Albrecht hasn’t held up to the scientific rigors of the last 50 years. The same is true of the other ratios of Ca/K and Mg/K.

In two weeks, I will share and summarize two published Nebraska field research studies conducted by Olson, Rehm, and Sorenson. 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