Soil pH is Higher in Some Areas Than Others 

Soil pH can change from state to state, but also within the same county and even in the same neighborhood. 

If you love growing Blueberries, Azaleas and Rhododendrons, and rubrum type Maples, or Pin Oak and they grow slowly with more yellow colored leaves, your site may have too high of soil pH.  It would be best to have the soil pH tested so that you know that is the problem.

Usually the chlorosis is exhibited in the leaf color being yellowing especially in between the veins on the leaves (interveinal chlorosis).  The veins are sometimes darker green then the rest of the leaves. 

Elemental Soil Sulfur is a Simple and Inexpensive Approach for Iron Chlorosis

A horticulturalist from a well known university suggested using:

"Encap® fast acting sulfur (49% sulfur, granular, sold in 2.5-pound bags).  It is applied by sprinkling on the soil surface at a rate of 2.5 pounds per 400-500 square feet.  I suggest application in early fall each year for at least 2-3 years or longer until remission of symptoms."