Soil pH has a profound influence on the availability of certain nutrients, especially if the pH is out of the 6.0 to 7.0 range. For example, we note that manganese becomes toxic below pH 5.5 and little will grow until the pH comes up. For those with pH in the 8.0 range, iron availability is an issue.
The chart below is helpful in pointing out how availability changes with pH.
The fuzzy lines between Ca, Al, Fe and P represent the effect these elements have on restraining the availability of P.
Chart redrawn from The Nature and Properties of Soils, 14th Edition by Brady and Weil.
