quite a few maple trees in my neighborhood have yellow leaves which seems odd in July/August. I was told that they may be suffering from chlorosis. These are 10 year old trees and I don't recall them looking like this in previous years. I googled the term and saw that high PH can cause this and suggests doing a soil test. How/where do you obtain such a test kit and if that is a potential cause do you remediate the situation. there are also plants at the base of the tree, so I'm also wondering if that could have upset some balance.
Adams County Colorado
There are several reasons that a maple’s leaves could be yellowing but your are correct that it is probably an iron deficiency. A couple of the common maple species including autumn blaze are prone to iron deficiencies when growing in the high pH soils which are common to Colorado's Front Range. If you want to have your soil tested you can find a submission form for CSU's soil's lab here: http://www.soiltestinglab.colostate.edu/documents/soilsample_horticulture.pdf You would mail the form along with a soil sample to the lab.
You can find a lot of information about iron chlorosis here: https://cmg.extension.colostate.edu/Gardennotes/223.pdf
The short version is that you will want to consider providing the tree with an iron fertilizer. Unfortunately not just any iron fertilizer will do. You will want to look for EDDHA iron as it is the most effective in our soils. This is a specific type of iron chelate. It is marketed under a couple different names. You can find this at many local garden centers or online retailers. You could also consider having an arborist treat the tree with iron injections. You can find more information about this treatment method at the above link.
I hope this helps, please let me know if you have further questions.