Answer: Based on your description it sounds like your soil has some clay in it; when you add sand to clay you essentially make brick once it dries out at all. Instead, you need to add copious amounts of organic matter. This will help the soil to hold both air and moisture and improve the structure. You could use chopped leaves, compost, old mushroom soil, aged manure and stable bedding, whatever you can get. You could work in as much as a ten inch layer and it wouldn't be too much -- but even a couple of inches will help, especially if you add more every year. An organic mulch such as straw will also help build the soil as it breaks down in addition to helping stop the soil surface from getting so hard.
It's impossible to tell you what type of fertilizer to use or what other amendments (if any) you might need to add (lime is a possibility for instance) without running some basic soil tests. You can purchase test kits or your County Extension (690-2655) can help you with the tests and interpreting the results.
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