In organic farming, a green manure is a type of cover crop grown primarily to add nutrients and organic matter to the soil. Typically, a green manure crop is grown for a specific period, and then plowed under and incorporated into the soil. Green manures usually perform multiple functions, that include soil improvement and soil protection: Historically, the practice of green manuring can be traced back to the fallow cycle of crop rotation, which was used to allow soils to recover.