It's Time to Cover your Soil

Dr. Ajay Nair
Assistant Professor, Department of Horticulture
Iowa State University

As the 2017 growing season slowly winds down, Iowa landscapes will soon be exposed to high velocity winds, rainfall (hopefully), and cold temperatures. Leaving our land and soil exposed to such environmental conditions elevates the risk of eroding our top soil. This is where cover crops come into the picture. Cover crops are crops that are primarily grown after a cash crop to cover the soil and protect it from erosion due to wind and rain. Apart from protection from erosion, cover crops perform various ecological services such as weed suppression, pest and disease reduction, nutrient recycling, and enhancement of soil biodiversity.

A cover crop that is well adapted and can be established well in to October is cereal rye (Secale cereale). Cereal rye should not be confused with winter rye (Lolium multiflorum) which unlike cereal rye should be seeded 45 to 60 days before freezing temperatures arrive. Annual ryegrass is more susceptible to winterkill, which could be due to lack of snow cover combined with wind chill and multiple freeze-thaw events. On the other hand cereal rye can be planted late in the season (even into October-November), however earlier planting is preferred. Seeding rate varies from 60-90 lb/A. Minimum soil temperature needed for germination of cereal rye is 38°F. Since soil moisture content is relatively low this year, for better results seed cereal rye before a rain event. This would guarantee good seed germination and stand establishment. Proper seed to soil contact is required to allow the seeds to absorb water for germination.  Optimal seed to soil contact is most often achieved by shallow tillage prior to placing the seed in the soil.  Avoid seeding into cloddy seed bed where seeds can fall into deep cracks that do not offer much contact with the soil.  Large clods can also cover seeds and prevent them from emerging. Cereal rye is an excellent winter cover crop because it rapidly produces a ground cover and provides following benefits:

1. Erosion control — Cereal rye reduces wind and water erosion. By having the soil held in place by its  roots during the fall, winter, and early spring, loss of soil from erosion is greatly reduced
2. Improvement of soil quality – Cereal rye roots does not contribute much to reduce soil compaction but it certainly improves soil tilth. Water infiltration is improved as well. Rye roots stimulate beneficial organisms in the soil, such as beneficial bacteria, fungi, and earthworms. Cereal rye could produce 2-3 tons of biomass (dry weight basis) and significantly contribute to increased soil organic matter.
3. Fertility improvements – Rye roots can take up excess nitrogen from previous crops and recycle the nitrogen as well as available phosphorus and potassium to the following crop. This is very important after manure application, because cover crops can reduce leaching of nutrients.
4. Suppress weeds – A dense stand of winter rye can suppress weeds by soil shading. Rye also produces allelochemicals that suppress germination and growth of weed plants in the spring.
5. Insect control – Beneficial insects, such as lady beetles or ground beetles, may be encouraged by a healthy stand of winter rye cover crop
6. No-till and strip-till opportunities – Cereal ryes provides opportunity for sustainable crop production through the integration of no-till and strip till techniques. Such initiatives improve soil building processes and also conserve soil organic matter. Crops such as pumpkins and  squash could be easily be grown using strip-tillage  techniques

Growers should also be aware of potential challenges with cereal rye. In the spring cereal rye could produce large amount of biomass which need to be managed appropriately. It could either be tilled or roller crimped. If roller crimping, roll only after the plant has reached anthesis (flowering) and the pollens begin to fly. Rolling before that will not kill cereal rye. Fresh rolled mat of cereal rye could attract armyworms that lay eggs in the rye residue. Also rye residue could attract seed corn maggots. Conditions that favor seed maggots include high levels of decaying organic matter and cool, wet weather. The flies can be attracted to fall-seeded seeded rye, or any other cover crop, that is disked down shortly (less than 3 weeks) before planting, although these insects could be easily managed with insecticides.  These disadvantages could be easily managed through timely and proper termination of cereal rye cover in the spring and scouting for insects. If tillage is used to terminate cereal rye, it is recommended to plant any vegetable only after 10-14 days to allow for disintegration of allelopathic chemicals and issues related to N-immobilization.