Effects of soil pH

Nutrient availability
The influence of soil pH on plant nutrient availability is demonstrated in Figure 20.4. It can be seen that for mineral soils the most favourable level for ensuring the availability of all nutrients is pH 6.5, while peat soils should be limed to pH 5.8 in order to maximize overall nutrient availability. In acid conditions some nutrients, such as manganese, and other soil minerals, such as aluminium, may become toxic.

Other effects on soil
Beneficial soil organisms are affected by soil acidity and liming. A few soil-borne disease-causing organisms tend to occur more frequently on lime deficient soils (see clubroot), whereas others are more prevalent in well-limed soils. Calcium sometimes improves soil structure and soil stability. It is probable that this is mainly because it encourages root activity and creates conditions favourable for decomposition of organic matter, yielding humus. Free lime in clay soils sometimes, but not always, leads to better crumb formation on drying and shrinking.