This is a 5-part series on the basic cation saturation ratio (BCSR) concept. Summary of Part 1 & Part 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.
There are two frequently referenced research studies from Nebraska related to the BCSR concept. The first was published in 1982 by Olsen and coauthors entitled “Economic and Agronomic Impacts of Varied Philosophies of Soil Testing” in the Agronomy Journal (link to abstract at https://doi.org/10.2134/agronj1982.00021962007400030022x) . The study was conducted at four locations (North Platte – Cozad silt loam/irrigated, Clay Center – Hastings silt loam/irrigated, Mead – Sharpsburg silty clay loam/irrigated, and Concord – Moody silt loam/rainfed) where researchers followed five (4 private and 1 state) different soil testing lab recommendations for continuous corn production over a period of 6 to 8 years in the late 1970s. All control plot soils in the top 6 inches had soil test potassium of 325 ppm or more. Potassium and magnesium recommendations varied by lab and location. It was not clearly stated in the study which individual lab or labs were using the BCSR concept for potassium and magnesium recommendations. Lab C only applied potassium or magnesium (not both) at each location/soil, suggesting they may have been using the BSCR concept. Concord had the lowest K saturation of 2.9% of the four locations and had a Ca/K ratio of 16/1 (13/1 recommended by Bear) and Mg/K ratio of 6/1 (2/1 recommended by Bear). Only potassium was recommended by the four private labs ranging from 42 to 175 lbs K/ac during the study period. No magnesium fertilization was recommended at this location. No corn yield differences were observed due to the potassium fertilization at Concord. This study was not only focused on the BCSR concept, but it did support other research that corn yields were similar across a broader range of ratios.
The second study was published in 1985 by Rehm and Sorensen entitled “Effects of Potassium and Magnesium Applied for Corn Grown on an Irrigated Sandy Soil” in the Soil Science Society of America Journal (link to abstract at https://doi.org/10.2136/sssaj1985.03615995004900060023x). The study was conducted over 4-years in Holt County on a Valentine loamy fine sand soil series. Potassium (30 lbs K/acre increments up to 240 lbs, potash) and magnesium (5 lbs Mg/acre increment up to 45 lbs as magnesium sulfate) were applied at different rates along with flat rates of phosphorus and zinc each year. Gypsum application varied so that each treatment was balanced for sulfur applied. The initial base saturation was 70% Ca, 17% Mg, and 7% K with Ca/Mg ratio of 4/1, Ca/K of 10/1, and Mg/K of 2.4/1. Early growth corn biomass and grain yield was the same for all treatments of potassium and magnesium over the 4-year study. Again, this demonstrates that similar corn yields can be achieved across a wide range of basic cation saturations (Mg and K increased to approximately 24% and 21% saturation correspondingly) and ratios.
In two weeks, I will share more specifics on the scientific consensus from two published literature reviews. 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
