I've been promoting The Biochar Revolution as the best and most comprehensive book on biochar for about five years now. It covers history, science, agriculture, production, and more. It's very good. Plus, it has several chapters written by pioneers in the biochar movement who have become friends of ours.
I just finished reading a new book: Terra Preta. If you are interested in biochar or just looking for a primer on it, this is the book you want. A quick and interesting read. It has recipes for turning biochar into terra preta, which is the end result we all want. "Terra preta" is portuguese for "black earth". It is the name for the soil found along the Amazon River basin, which is the richest soil on the planet. And the richer and healthier the soil, the healthier the plants, and the more wholesome and nutritious the produce. This is the whole basis of organic gardening/farming. Pretty simple. Just another piece of the puzzle from the ancients that we are relearning.