Definition - What does acidity mean?
The acidity of soil can be measured using a pH test. Some crops grow well in acidic soil and others require a neutral pH to flourish. Acidic soils feature basic elements such as potassium, magnesium, calcium, and sodium. The soil colloids are replaced with hydrogen ions in the acidic soil. Acid soils usually form in areas with a high rainfall. The soil in the American Southeast tends to be far more acidic than soils found in the West or Midwest.
MaximumYield explains acidity
Soils become acidic when basic elements such as calcium, magnesium, sodium, and potassium held by soil colloids are replaced by hydrogen ions. Soils formed under conditions of high annual rainfall are more acidic than are soils formed under more arid conditions. Thus, most southeastern soils are inherently more acidic than soils of the Midwest and far West. Regions of the country that have low rainfall usually have a soil pH reading of around 7.0. Certain plants such as legumes increase soil acidity. In some regions of the country the top six inches of soil may have a neutral pH level but then the lower layers are very acidic. The soil's pH balance can be checked using a simple pH test kit.