Green Manure—Crops That Improve
Soil Structure and Add Nutrients

Green manure is a crop grown primarily for its nutrients. When plowed under, these crops add nutrients and organic matter to the soil.

Organic farmers consider these crops to be an essential part of the farm ecosystem. No-till farmers keep the crop mowed and leave the foliage on ground to decompose over time.

Green manure can be from many field crops. Legumes are often used.

These include alfalfa, sweet clover, white clover, peas, black medic, red clover and indian head lentils.

Vetches are also used to add nitrogen and better the soil.

Oats, forage grasses, fall rye, buckwheat and barley can be used as well, although they don't add much nitrogen to the soil.

Cover crops help control pests, add needed nutrients, and improve the soil with organic matter.

They also control soil erosion, reduce soil compaction, and increase the activity of soil organisms.

If grown at the correct time, green manure crops also help control weeds, and stop some insect and plant diseases cycles. They also provide a habitat for bees, parasitic wasps and other beneficial insects.

Crops like mustard and yellow sweet clover produce a toxin that retards germination of weed species. Fall rye has been known to also retard germination of wildflowers (so don't use it as a cover crop in any plot where you plan to grow wildflowers.

Manure crops are most valuable to the soil while they're still green. Till them into the top 3 inches (7.5 cm) of the soil to ensure quick decomposition. Till late green manures in the fall to provide the most nitrogen in the spring.

The micro and macronutrients from green manures will remain available for a number of years after the microbes break down the plants.

The decomposition process releases acids that will lower the pH of the soil and increase the amount of phosphorus available to your plants. (This also means that you'll need to temper the acidity with lime or another form of calcium if your soil is already fairly acidic.)

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