Low pH in soil is a problem for agriculture and the environment because it can affect plant growth through its effect on plant nutrients and soil biology
Some nutrients may reach toxic levels, while others can become insoluble (therefore unavailable), leading to deficiencies. The changes in the solubility of plant nutrients associated with increasing soil acidity are:
Some plants are more sensitive to aluminium than to manganese and vice versa. For example, white clover is tolerant of aluminium but sensitive to manganese. Often the cumulative effects of low pH and various toxicities/deficiencies result in the greatest damage.
The degree to which soil acidity affects nutrient availability and therefore plant health and growth depends on pH level, soil type and soil organic matter levels.
Sometimes the effect of acidic soils on the growth and production of crops and pastures is not direct, but rather through the effect on soil micro-organisms, that in turn affect plant growth. Soil organisms are influenced by soil pH.
Soil pH influences both survival and functioning of Rhizobia.
The fungus that causes the root disease Take-all in cereals, Gaeumannomyces graminis var.tritici, is most active in soils with a pH(CaCl2) greater than 4.8, and has a low level of activity in soils with a pH less than 4.6. Liming greatly increases the activity of Take-all.
Farmers and land managers will see evidence of the above expressed as:
Remember general signs that may point to soil acidity can also be the result of other land degradation issues:
* Reduced yields from acid sensitive crops and pastures
* Poor establishment of perennial pastures
* Failure of perennial pastures to persist