Cover crops
From Appropedia
Managing Cover Crops Profitably, 2nd Edition - Download this 212 page book free as a PDF file.
"Managing Cover Crops Profitably" explores how and why cover crops work and provides all the information needed to build cover crops into any farming operation. This is the most comprehensive book ever published on the use of cover crops to sustain cropping systems and build soil.
http://www.sare.org/publications/covercrops.htm
