Green manures, crops grown especially for returning to and improving the soil, have a long, mainly agricultural, history. Such as lupines, usefully a Nitrogen fixing legume, were grown and dug under as far back as Roman orchards. The Medieval fallow continued an ancient break in cropping combined with a green manuring by weeds. Excellent from the weeds point of view as they got to seed and multiply every few years just as the last batch faded away.