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  A Publication of UVM Extension's Vermont Vegetable and Berry Program

Winter Rye: A Reliable Cover Crop

by Vern Grubinger
Vegetable and Berry Specialist
University of Vermont Extension

Why Rye? Cereal rye is an excellent winter cover crop because it rapidly produces a ground cover that holds soil in place against the forces of wind and water. Rye’s deep roots help prevent compaction in annually tilled fields, and because its roots are quite extensive, rye also has a positive effect on soil tilth.

Compared to other cereal grains, rye grows faster in the fall and produces more dry matter the following spring--up to 10,000 pounds per acre, although 2 tons is more typical in the Northeast. Rye is the most winter-hardy of all cereal grains, tolerating temperatures as low as -30°F once it is well established. It can germinate and grow at temperatures as low as 33°F, but it sure won’t grow very much when it’s that cold.

When sown in late fall, around the time of the first light frost, winter rye is still able to put on just enough growth to provide some protection against soil erosion over the winter. High seeding rates should be used for late-sown winter covers to assure a decent amount of ground cover, since individual plants will be small.

Growing Rye.  Cereal rye thrives on well-drained loamy soils but it’s tolerant of both heavy clays and droughty, sandy soils. Rye can withstand drought better than other cereal grains, in part because of its prolific root system. It grows best with ample moisture, but excessive rainfall can suppresses subsequent vegetative growth and flooding can it. Rye can grow in low-fertility soils where other cereal grains may fail. Optimum soil pH is 5.0 ­ 7.0, but pH in the range of 4.5 ­ 8.0 is tolerated.

Suggested seeding rates are 1 to 2 bushes per acre if drilled, 1.5 to 3 bushes per acre if broadcast and lightly tilled in. A bushel of rye is said to weigh 56 pounds. It’s best to use seeding rates on the high side if planting into a rough seedbed, seeding late in the fall when growing time will be limited, or trying to establish rye on a field that has a high potential for erosion. Rye is more sensitive to seeding depth than some other cereals, and it should not be sown more than 2 inches deep.

Rye will often respond to a modest application of nitrogen (N) fertilizer, but when it follows corn and other crops that have been well-fertilized with N it seldom requires additional fertilizer. Rye has a good ability to scavenge residual soil N when it follows other crops, and it is commonly grown for this purpose. This reduces the potential for nitrate leaching into groundwater and it conserves N fertilizer inputs, which saves money.

Flowering in rye is induced by 14 hours of light in spring. Vegetative growth stops when reproduction begins. If allowed to grow to maturity, rye residues tend to have a high carbon to nitrogen ratio and high percentages of lignin and cellulose, so they can be slow to decompose.

Excessive amounts of spring residue produced by rye can delay cash crop planting and actually decrease the availability of N to subsequent crops as N is tied up or ‘immobilized’ by the decomposing residues. To avoid these problems, and to avoid ‘grow-back’ of the rye, it is best to thoroughly incorporate it when it is between 12 and 18 inches tall and still relatively succulent. In some years wet spring weather may prevent timely field operations, resulting in larger amounts of rye residue than desired.

Rye plus Legume.  Winter rye can also be grown in mixtures with a legume such as hairy vetch and/or crimson clover. During the fall and winter, cereal rye protects the soil, scavenges soil-N, and acts as a nurse crop for the legume. In spring, rye provides structural support for the climbing legumes. The relatively high N content of legumes reduces the overall C:N ratio of the rye/legume mixtures, and increases the nitrogen available to the following crop.

When growing a winter rye and legume mixture, the rate of winter rye seeding should be reduced to no more than a bushel per acre to allow space for the legume to grow. A seeding rate of about 20 to 30 pounds of hairy vetch per acre is recommended. The mixture should be sown several weeks before the typical first fall frost date to allow time for the legume to adequately establish so it can survive the winter.

In winter hardiness zones 6 and above, about 10 pounds of crimson clover can be added to the mix above, or the clover can be sown at 15 to 20 pounds per acre in place of the vetch. In fields where they have not been grown before, legume cover crops should be inoculated with the proper Rhizobium bacteria to be sure that root nodules are formed and nitrogen fixation takes place.

A mixture of hairy vetch plus rye can produce a lot of biomass that can enhance soil quality while providing a significant amount of nitrogen to a subsequent crop. If a fine seedbed is needed the following spring, it may be better to mix hairy vetch with oats, which winter kill in northern locations, since there will be less plant residue to deal with than will be the case with mature rye stems

Allelopathic Effects.  Cereal rye produces several compounds in its plant tissues and releases root exudates that apparently inhibit germination and growth of weed seeds. These allelopathic effects, together with cereal rye's ability to smother other plants with cool weather growth, make it an ideal choice for weed control.

However, allelopathic compounds may suppress germination of small-seeded vegetable crops as well if they are planted shortly after the incorporation of cereal rye residue. Large-seeded crops and transplants rarely are affected. There is some evidence that the amount of allelopathic compounds in tillering plants is lower than in seedlings.

Rye for No-Till.  Because it leaves a lot of residue on the soil surface, no-till rye can be an effective way to avoid erosion and help control weeds. Mowing or using a burn-down herbicide are two common methods of killing a rye cover crop for no-till plantings. To kill rye by mowing, it should be done at flowering when the anthers are extended, and pollen falls from the seed heads when shaken. If mowing is done earlier, the rye simply grows back. Studies are underway looking at rolling instead of mowing as a means of physically killing winter rye.

For no-till to be effective, it’s important to first grow a very good stand of rye before killing it. When rye is left as a surface mulch it is difficult if not impossible to manage escaped weeds with mechanical cultivation. Thus, a poor no-till cover may be worse than no mulch at all in terms of weed management.

Research at Penn State, Michigan State and elsewhere has looked at the use of a roller-crimper to mechanically kill winter rye for no-till crop production.

Grow your own Mulch.  Some growers harvest winter rye to be used for mulching strawberries over winter or for mulching to suppress weeds between vegetable crop rows. Rye can provide a very clean mulch so long as it is cut before any viable seed is set. After mowing it should be allowed to thoroughly dry in the field and then baled using traditional baling equipment.

These windrows of rye will be baled and stored for mulching strawberries over the winter.

To learn more about using winter rye and other cover crops, get the book Managing Cover Crops Profitably. It is available for free as a pdf or order online at: http://www.sare.org/Learning-Center/Books/Managing-Cover-Crops-Profitably-3rd-Edition.

To view video clips of vegetable farmers in the Northeast describing their cover cropping techniques, go to: http://www.extension.org/article/18439.

Last Updated: October 2010
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