greenmanure

Green manure refers to a class of crops that are grown primarily to be incorporated into the soil rather than harvested for food or fiber. These crops, typically legumes, grasses, or brassicas, are sown to improve soil fertility, structure, and organic matter content. After a growth period ranging from a few weeks to several months, the plants are plowed under or otherwise mixed into the topsoil, where their biomass decomposes and releases nutrients.

The main benefits of green manuring include the addition of nitrogen—particularly from legume species that fix atmospheric nitrogen through symbiotic rhizobia—enhanced soil moisture retention, suppression of weeds, and protection against erosion. Organic matter from the decomposed plants contributes to soil aggregation, which improves aeration and root penetration. Increased microbial activity associated with the added organic material can also aid disease suppression and nutrient cycling.

Common green manure species comprise clover, vetch, rye, oats, mustard, and radish. Selection depends on climate, soil type, and the specific agronomic goals of the farmer. In temperate regions, cool‑season grasses are often used in winter, while warm‑season legumes dominate in summer rotations. Management practices such as timing of incorporation, moisture conditions, and residue length influence the rate of decomposition and nutrient release.

Green manure has been employed for centuries in traditional agriculture and was promoted in the early 20th century as part of sustainable farming movements. Modern interest has grown alongside organic and regenerative agriculture, where green manure is integrated with cover cropping and reduced tillage to maintain soil health and reduce reliance on synthetic fertilizers. Limitations include the need for additional land or adjustments to existing crop schedules and the potential for temporary nitrogen immobilization if incorporation is mistimed.