Are you quite sure that legumes don't fix nitrogen? Your Grandfather was a very scientific farmer, and he taught me that alfalfa does fix nitrogen in the soil. To understand my confusion, I'd refer you here http://www.springerlink.com/content/b6695q9r26kv8670/ or here http://en.wikipedia.org/wiki/Nitrogen_fixation There's a National Geographic Channel show coming on at 9pm on November 20 that deals with the lost cities of the Amazon, and references terra preta, by the way.