Grass–Legume Combinations

Many farmers grow mixtures of cover crops to multiply the benefits of a planting. The most common approach is to grow legumes and grasses together. Some popular combinations include hairy vetch or red clover plus winter rye in cold-winter areas, or bell beans plus oats in milder-winter areas. A legume–grass combination offers several benefits:

Bell beans plus winter rye & oats

This cover-cropped field of bell beans, with a nurse crop of winter rye and oats, was a trial to evaluate nitrogen-fixing fall-cover options. The bell beans are starting to bulk up and to some degree the oats/rye has suppressed annual weeds. Planting date: September 2. Image date: October 20 (approximately 7 weeks). Albion, Maine. Latitude: 44.4°N.

• Legumes and grasses grown together balance the carbon-to-nitrogen ratio in the soil after plow-down. The legumes, rich in nitrogen, break down quickly, while the carbon-rich grasses take longer to decompose. Growing the two together makes nitrogen available to help break down the grass residue and reduces the amount of time that must elapse before a subsequent crop can be planted.
• A faster-growing crop such as oats or winter rye serves as a nurse crop to shelter less-robust, slower-growing plants such as red clover or sweet clover. Grasses establish quickly and prevent the growth of weeds that would otherwise compete with the legume.
• Low-growing crops and taller crops planted together cover more of the soil and do a better job of preventing erosion and weeds than a single crop alone. Sorghum grows tall, and cowpeas grow low; together they shade the soil and prevent weed seeds from germinating.
• Legumes augment nutrient content of a hay crop that is to be used for livestock.
• Combinations of cover crops reduce the risk of crop failure and allow for differences in conditions across a field. In spots where a legume doesn't establish well, the grass may do better and vice versa.

Further Reading

• Cover Crop Decision-Making Tool • 5 Steps for Deciding What to Plant When & Where
• An Introduction to Cover Crop Species for Organic Farming Systems, from the eOrganic network.
• Overview of Cover Crops and Green Manures, by ATTRA, the Sustainable Agriculture Information Service.