What is base saturation?

The Analysis page of your SoilKit report includes many insights into your soil's nutrient status and soil health properties. One common question we get, even from those who are already familiar with essential soil elements, is about the final section of the SoilKit report: Base Saturation. What is it and why does it matter?

Understanding base saturation goes back to the soil's cation exchange capacity (CEC). CEC is basically the soil's total potential for holding nutrient cations, which are elements in a simple form that can interact with plant roots (not locked away inside soil minerals or chunks of organic matter). Cations can be acidic or basic (alkaline). The main nutrient cations in soil are all basic: calcium (Ca), potassium (K), and magnesium (Mg). Your SoilKit results include both the amount measured for each nutrient (for example, in parts per million or lbs/acre) and the percentage each nutrient represents of the soil's total CEC. This is important for understanding how the different elements present interact with each other in the soil. For example, 150 ppm of potassium could turn out to be 4% saturation in a sandy, low-CEC soil but less than 1% saturation in a clayey, high-CEC soil. Elements with extremely low percent saturation could have low absorption by plant roots, even if the element level itself is considered sufficient. 

So how exactly do element saturation percentages relate to acids, bases, and soil pH? Soil nutrient cations, as well as sodium (Na), are all basic (alkaline). The percentages of these elements in your soil's CEC are added together to calculate the total base saturation. The remainder of the CEC is filled up by acidity, represented in your test results by the element hydrogen (H). Because of this relationship, high acidity, low pH, and low base saturation tend to go together, while low acidity, high pH, and high base saturation tend to go together. This explains one reason why high acidity (too low pH) can be detrimental to plant growth: it corresponds with low base saturation and low availability of nutrients that plants need from the soil.

Still have questions, or need support understanding all the numbers in your soil test results? Check out our reference guide for soil properties and elements to learn more, or arrange an Expert Consultation with a SoilKit team member for individualized support!