MSU Extension Soil Web pages for Consumers

This chart shows how pH, the alkalinity or acidity of soil, affects availability of nutrients. Notice that most of the colored bands are widest, indicating more of the nutrient is available, at pH range 6-7.

As this indicates, most nutrients are more available, chemically, in the soil at this optimum growth range for most plants.  Where soils are more acid or alkaline, a nutrient deficiency symptom is more likely to appear even if the nutrient is present in the soil, because the plants cannot chemically extract it.