Hi James,

Thank you for contacting the UNH Extension Infoline.

There could be a couple of reasons why your maples are beginning to turn color. I've checked a variety of resources and found a good article that might help you determine the cause.
https://www.canr.msu.edu/news/early_fall_color_in_trees_and_shrubs_may_be_a_sign_of_stress

You also wondered if iron chlorosis might be the cause. Here is an article that gives you some info about that: https://extension.usu.edu/forestry/trees-cities-towns/tree-care/preventing-iron-chlorosis

If you decide to have your soil tested, this link will provide all the information needed to have that done at UNH Extension: https://extension.unh.edu/agriculture-gardens/pest-disease-growing-tools/soil-testing-services Here is the specific soil testing form for Home Grounds & Garden: https://scholars.unh.edu/cgi/viewcontent.cgi?article=2783&context=extension&preview_mode=1&z=<personal data hidden>

Please reach out if you have other questions.