What are the Benefits of Cover Crops or Green Manures?
Cover crops and green manures are basically the same term. When these plants are alive they are cover crops. When the plants are decaying they are green manures. Green manuring has all the soil benefits of classic composting, plus other benefits:
- Green manures can fertilize large acres of land cheaper and easier than hauling in tons of finished compost.
2. You can eat the produce of certain cover crops like beans, peas, or radishes. It is harmful to humans to eat compost!
3. The roots of certain legume green manures can supply tons of free atmospheric nitrogen per acre to the topsoil after the cover crop plants are tilled, mowed down, or smothered. Rhizobacteria live inside the legume roots creating a unique relationship that actually converts atmospheric nitrogen into organic nitrogen for the legume to use. This extra nitrogen fixation built up by the rhizobacteria can not be beneficial to other plants near by, or future crops in the soil next season, until that legume is dead and recycled into the soil by the green manuring process. Compost can't fix nitrogen in the soil.
4. All green manures supply extra organic matter to feed and breed beneficial soil organisms for soil fertility and soil health.
5. The roots of certain cover crops can go down several feet below the topsoil and into the subsoil to break up hardpan and pull essential nutrients up to the topsoil level at green manuring time. After 24 months of continuous growth, alfalfa roots can extent over 20 feet down, that can turn it extra OM down into the subsoil! No regular tractor or mechanical tiller can plow that deep! Without tilling it in, compost can't do that.
6. Some cover crops can weed out other plants. Buckwheat, oats, and sunflowers are good types of these allelopathic plants.
7. Some cover crops can attract beneficial insects and repel bad insects like marigolds and crimson clover. Compost can't do that either.
8. Some special cover crops can help control diseases in the soil or on the foliage of nearby plants. Examples are garlic, onions, hot peppers, basil, marigolds, thyme, and other herbs. These plants can protect plants like tomatos from diseases. They can also control bad nematodes or other soil problems. Some of these cover crops can do these functions as living plants or as decaying green manures.
9. Some legume cover crops, like white clover, can be planted next to your crops during the warm season to be used as a living mulch.
- Green manures work best when mixed with legumes and non-legumes. That way you get the nitrogen fixing benefit from the legumes, but also you maximize the fast growth of the expansive root development and tall foliage height that is characteristic of grasses and grains.
- Did you know that about 95% of all the bulk and biomass of all non-legume cover crops is a direct production from only water and photosynthesis! The other 5% is straight from the soil. Legume cover crops go farther...