I saw a list of proposed topics for an upcoming turfgrass conference, and under the heading of soil fertility was included base saturation. I immediately thought of this paragraph from Murray McBride’s Environmental Chemistry of Soils:
If the ill-defined nature of exchangeable acidity were not enough to discourage attempts to universally apply the concept of percent base saturation, it is found that many soils composed largely of variable-charge minerals (particularly highly weathered soils) have ill-defined and quite low CEC values. The estimates of exchangeable Al in these soils depend on the properties of the cation used to displace Al. Much of the Al release and adsorption that occurs in soils of this type may be controlled by processes other than cation exchange, such as precipitation and dissolution, making the base saturation concept misleading or even irrelevant. Given these facts, percent base saturation seems not to be a particularly useful concept, and might be better replaced by separate measures of exchangeable base cations and exchangeable Al. This point of view is strengthened by observations that the phytotoxicity of acid soils is correlated better with soluble free Al3+ than with percent base saturation.
I hope this “misleading or even irrelevant” topic is not discussed at the conference.
Somewhat related to this, about pH and Al: