A Natural Farming System For Sustainable Agriculture In the Tropics Sustainable Agriculture Book - Chapter 11 Green Fertilizers
Green fertilizer is Fundamental #5. It feeds the next crop efficiently. As you plow crop residue into the soil it will eventually become humus and fertilizer for following crops. It is a form of composting, in which materials do not need to be transported to a mixing/composting site. You could call it field composting.
Economical on a large-scale, green fertilizers will build up the organic matter in the soil. Many of the professional farmers grow a crop to flowering and plow it under before fruiting. This will maximize the biomass and minimize nutrient and energy loss.