Oh, that's really cool! I have a stellar recommendation for you. There's nothing like connecting to the earth and touching the soil like so many of our ancestors did for the brunt of our history.
The book is called "The Soul of Soil." by authors Joseph Smillie and Grace Gershuny. It's nearly a booklet, a little less than 200 pages. It's so brief, but you'll learn about soil's affect on plants in an easily-digested way from an excellent source. Here's an Amazon link.
It must be out of print, I know it was updated in 2009. The price goes up every time I look at it. You'll want to keep one for yourself as a reference even though you'll be so tempted to give it away. People never want to give them back!