Green manure. In agriculture, green manure is created by leaving uprooted or sown crop parts to wither on a field so that they serve as a mulch and soil amendment. The plants used for green manure are often cover crops grown primarily for this purpose. The major difference between compost and green manure lies in their composition. While green manure is made from animal-based waste products such as urine and feces. Adding compost to the soil enriches the soil with organic matter while green manure increases the nitrogen level of the soil.