What is base saturation?
Base saturation refers to the proportion of the cation exchange sites in the soil that are occupied by the various cations (hydrogen, calcium, magnesium, potassium). The surfaces of soil minerals and organic matter have negative charges, that attract and hold the positively charged cations. Cations with one positive charge (hydrogen, potassium, sodium) will occupy one negatively charged site. Cations with two positive charges (calcium, magnesium) will occupy two sites. Base saturation does not have any relation to fertilizer recommendations for the negatively charged nutrient ions, like phosphate, nitrate and sulfate. To determine the base saturation, you must first know the cation exchange capacity, which is a measure of the amount of negative charge in the soil. To determine this precisely, the soil is saturated with an unusual cation like barium, to displace all of the other ions, and then the amount of barium sticking to the soil is determined.
