I think some of the most productive soils are organic soils, although they aren't that common and the next is loams--silt or clay loam. In eastern climates, soils often tend to be more clay. Sandy soils tend to be less fertile because they don't hold nutrients or water as well.

In any case, people usually have a limited ability to choose the soils available and take the soils available in the area they choose to live. Mainly you would avoid purchasing land that has soil problems such as salinity, wetness, or gravelly/rocky. In an eastern climate, there may be other soil factors you would want to avoid but I think these apply pretty universally.

Check out the ag school at your state university for their soils department and look for information there, or check the USDA Natural Resources Conservation Service Soil Survey site for information on soils and soils maps of your area. When you have a piece of land in mind, then stop in at your county NRCS office and talk to them about the soil type(s) on the property and their suitability for what you want to do.

On the web?

I'd start looking up universities that have a good ag program, browsing through course offerings and finding the courses for soils, then seeing if the professor has put a reading list on the web, and haunt the local bookstores or libraries.

Short of that, when I want to sleep, I have a text from college called Soil Fertility and Fertilizer. It reads like a chemistry text (which is what it is, an applied study of the pure science of chemistry).

It'll give an electron's eye view of what is happening inside what we call soil.

Find the County Extension office of your nearest Ag University. (It's OSU in Oklahoma.) The extension office is usually at your county fairgrounds. They can take a soil sample and analyze it for you, suggesting what you need to add to your specific acreage's soil to grow any particular crop you are interested in. Good luck!

Mustang

Sounds like you are in SC? If so go to the Clemson extension web site.