How is soil"corrected" to pH 6.5? What fertilizers do peach trees want? How do I determine how much to water peach trees? If leaves turn sort of yellow, am told they needed iron. Is this right? Thank you.
Correcting the pH to 6.5 requires that you know what pH you're starting with. If you don't know, you can have a soil test done by the county extension service (This link will help you find the nearest office:
https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm ) or you can buy an inexpensive home test kit in any plant store. The home test is not as exact, but it will give you a general idea. Once you determine the existing pH, you can add certain minerals to either raise or lower it, but be aware any changes will take several months to a year. These articles tells you more about pH: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
Yellowing leaves can be caused by many things, but iron deficiency is usually signaled by yellowing between the veins, while the veins stay green. This article has more information on that: https://www.gardeningknowhow.com/plant-problems/environmental/leaf-chlorosis-and-iron.htm
You've also asked about peaches. Here are some articles to help with your basic knowledge: https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-care.htm