green manure 
noun [mass noun]
A fertilizer consisting of growing plants that are ploughed back into the soil.Stephen Leblanc uses cow manure, green manure and crop rotation to ensure nutrient-rich soil for his rapeseed crop....
- Under organic management, fields received cover crop green manure as well as periodic dairy manure applications.
- Out of these sources only farmyard manure and green manure are widely used.