Moving chickens over a buckwheat paddock.  The birds knock the green manure over, crimp it, eat the buckwheat seeds, and add a layer of manure to be absorbed by the carbon; then after the first rain, the buckwheat seeds the chickens missed sprout to add a second crop of buckwheat.  After a second pass, and a third germination, frost kills the buckwheat before it can set seed, so it never becomes a problem in the spring garden.