|MadSci Network: Agricultural Sciences|
Not all volcaanicn soils are more fertile because the ash that comes from volcanoes differs in its mineral content and in its physical properties. However volcaninc soils are often more fertile because they are relatively unweatherd. They have not undergone extensive leaching and they tend to contain more of the basic cations that plants require. These include Mg Ca K Older soils have less of these because they are leached out by water percolation As this leaching ocurs, soils often get more acidic. An increase in acidity often results in a decrease of availability for many essential nutrients and a corresponding increase in the concentration of nutrients that may be dangerous or toxic to plant, such as alumunium. So the answer to your question is that many volcanic soils are relatively younger thatn other soils and have greater amounts of essential nutrients that make them fertile.
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