Matthew F. Stephens
County Agent, Jackson Parish
Cover crops are grasses, legumes or small grains grown between fall and spring for the purpose of protecting and improving the soil. The most common cover crops in Louisiana are fall-seeded cereals, such as rye or wheat, and fall-seeded annual ryegrass. Spring oats also are sometimes used. Fall-seeded legumes, such as hairy vetch, Austrian winter peas and different clovers, may also serve as soil enhancers and erosion inhibitors but are mostly used as food sources for wildlife.
Whether one is planting cover crops for wildlife habitat, agricultural, urban, forestry or construction purposes, this is a great way to prevent erosion and protect water quality while enhancing the soil. The following is a short explanation of some of the advantages of using cover crops.
Advantages of Using Cover Crops
Water erosion control. This is one of the two major reasons for growing winter cover crops in Louisiana. Older research has shown that fields with winter cover plowed under in the spring have 55 percent less water runoff and 50 percent less soil loss annually than do fields with no winter cover. More recent studies show soil losses from corn or soybeans no-tilled into a vigorous growth of rye or wheat to be 90-95 percent less than soil losses from corn and soybeans conventionally tilled. This also applies to yards, construction sites and reforestation.
Improved soil tilth. Debris from plant material, also known as biomass, adds organic matter to the soil. Organic matter helps the soil to retain more moisture, gives a liming effect and increased the porosity of the soil. The added organic matter from a winter cover crop, whether turned under or left on the surface, would benefit nearly all Louisiana soils but especially those having less than 2.5 percent organic matter.
Cover crops recycle nutrients that might otherwise be lost to leaching during the winter and spring. Also, cover crops provide excellent surface mulch after being killed with a contact herbicide; the mulch not only reduces soil erosion but also slows evaporation of soil moisture, increases infiltration of rainfall, increases soil organic matter and aids in control of annual weeds. Additionally, cover crops can often be grazed by ruminant animals in the early spring before other permanent plants are established.
Improved plant performance. In recent experiments, winter cover used with no-till planting markedly increased corn yield. For instance, three-year average continuous corn yields were 8 bushels per acre greater when planted into a winter cover of rye and 25 bushels per acre greater when planted into hairy vetch than yields from plots without winter cover. The significantly higher yield in the hairy vetch cover plots was due primarily to the extra nitrogen (N) that this legume provides. Even though the experiments were done on corn, the principal remains the same regarding lawn grasses, pastures or garden areas.
Spring Management of Cover Crops
For maximum soil and moisture conservation and the greatest tilth improvement from a cover crop, delay as long as possible killing or plowing it under in the spring. If the nitrogen from legumes is your main reason for planting a cover crop, then all of the plant material should be plowed under of mulched to gain the full affect of legume’s nitrogen.
Annual ryegrass should not be allowed to remain growing once the permanent grass (either yard or pasture) is attempting to come out of dormancy and should be mowed or cut for hay as soon as the permanent grasses begin to “green up”. Summer perennials such as Bermuda grass can suffer major stand losses due to the annual ryegrass’s shading and smothering properties.
Selecting Cover Crops
Ryegrass and certain cereals like rye or wheat are the most popular cover crops in Louisiana for a number of reasons. They are easy to establish and fast growing, and seed is readily available and relatively inexpensive. Legumes, on the other hand, do not provide cover as rapidly, but they do supply some nitrogen that can be used by your summer plants. Certain soil characteristics, such as soil pH, are extremely important to legumes and not as critical with cereals and ryegrasses.
Weigh the relative importance of the above factors in choosing the "right" cover. Some situations may not see any advantages to cover crops due to a healthy root system that holds the soil intact throughout the winter months. If the yard, pasture or field has “bald” spots, a cover crop will be advantageous for many reasons.
Contact your local LSU AgCenter office for more details on cover crops and the right cover crop for your individual needs.