Base Saturation

To determine the base saturation first we need to know the “Total exchange capacity”, this will tell us the nutrient holding ability of your soil.

We must then measure the percentages of each of the main Cations - Calcium, Magnesium, Potassium and Sodium and adjust them to the ideal levels that will help grow crops and pastures to their maximum potential.

This will also improve the environment for the soil biology, which is absolutely critical in the processing of nutrient for plants. Many minerals are not available to plants directly and need to be ‘reduced’ through a biological process to change them into plant available forms.

It is not about flooding the soil with any one element but rather a balancing act of all essential minerals. Look at the most limiting nutrient first ‘Law of the minimum’ when prioritising budget, then the next limiting, and so on.

Magnesium levels need to be adjusted to a specific base saturation percentage (see graph below)

Not enough magnesium means a deficiency to the plant, but if the magnesium level climbs to high this can also limit uptake.

Calcium should occupy the most sites on the soil colloids and is the king of all nutrients. 

We must try and achieve the ideal BS of calcium as an excessive liming programme will increase calcium levels to a point where it may ‘tie up’ other elements.

Potassium is another of the main nutrients to have in the right B.S. percentage. Ideally 5% is the excellent level or up to 7% for woody crops like grape vines or fruit trees.

It is very important to have Potassium levels higher than Sodium as the plant will take up whichever one is at the higher level. We therefore want to avoid excessive Sodium uptake which may cause cell degradation (wilting) and yellowing in crops.

When micro nutrients are present in the soil in adequate amounts, and the soil has the right base saturation percentages, they are at their most available. 

It is not correct to say balance the soil and micronutrients will take care of themselves; some soils simply do not contain adequate amounts of micronutrients. However, if they are already there and tied up by excesses, they will be released as the excesses are brought under control.

Listed below are the optimum cation base saturation percentages for most soils.

Base Percentage


True soil balance means determining and adding the proper amount of each nutrient only when required. Fertility is the balance between all elements. Not only is each element necessary individually, but a balance of all these elements is necessary ‘collectively’.

Achieving the above means improved nutrient availability and proper plant nutrition.