Temporary grasses stabilize soil
Man-made disturbances, such as roadside or reclamation projects, can result in serious soil-erosion problems, destroying the soil profile and adversely affecting the surrounding natural habitat. Temporary cover crops are a popular strategy because they reduce the threat of erosion, aid restoration efforts by establishing the nutritional base necessary for re-vegetation and offer a soil-root matrix to anchor naturalizing plants.
By definition, a temporary cover is vegetation you seed onto a site to provide soil stabilization for 2 to 12 months until you can sow the permanent "crop." You may need to stabilize soil for longer periods, but you must be careful that the temporary cover you use does not out-compete desired permanent vegetation once you plant it.
People often ask me about suitable temporary crops during revitalization of roadside or reclamation projects. The need for such crops may arise if problems delay a permanent reclamation seeding beyond the preferred seeding dates. The temporary cover will hold and contain soil from erosion loss until construction resumes. Using temporary cover crops is environmentally proactive, keeping the site from exposure to the elements for a prolonged period, risking serious soil erosion.
Temporary covers provide numerous benefits: * They serve as barriers protecting the soil surface from wind and water erosion. * Organic matter from the cover crop's active root growth retains moisture, protects the soil structure from compaction and allows water and nutrients to penetrate the soil. * Temporary covers limit pesticide and fertilizer runoff. * They increase beneficial nutrients in the soil (especially if you use them as a green manure crop) and improve microorganism activity within the soil profile. Lastly, temporary covers can reduce weed populations and may improve animal-habitat preservation.
Soil-conservation research has documented the merits of a temporary stand for preventing soil loss. The more quickly you cover the site with temporary vegetation, the less damage will occur to the site's integrity. To select the most appropriate temporary cover, consider site location, time of year, soil characteristics, anticipated precipitation and intended use of the site. A reputable supplier can be of great help in the selection process.
Good seed-to-soil contact is necessary for enhancing seed establishment . A sterile fiber mulch or clean straw protects germinating seed. Also, consider the seed quality of the temporary crop. Grains, grasses and mulch covers not screened for weed content can cause future problems depending on the sensitivity of the site.
Characteristics of temporary covers vary by species, of course. However, in general, they exhibit several common traits that make them appropriate for this use: rapid germination and seedling establishment, good lateral growth, slow vertical growth and tolerance of droughty and infertile soils. Non-native annual grasses such as annual ryegrass-which might be too aggressive for native landscapes-may be suitable for vegetating disturbed sites during a re-vegetation process.
Numerous species qualify for use as temporary cover crops. According to the 1994 U.S. Department of Agriculture (USDA) Handbook No. 170 (available through the U.S. Government Printing Office), more than 120 improved cultivars of grasses, legumes, herbs and shrubs are available for use in soil stabilization. Annual grasses, cereal grains and legumes are the most common choices for temporary crops, although some perennial grasses also are suitable. Permanent stabilization projects often specify a greater diversity in perennial grasses, forbs and legumes than for temporary cover. In this article, I mostly will discuss grasses for temporary use.
Annual grasses *Annual ryegrass. Many landscapers consider annual ryegrass (Lolium multiflorum) as the grass of choice for soil stabilization. Recognized also as "domestic" or "Italian" ryegrass, it is an economical addition to cool-season perennial-turfgrass seed mixes to bulk up the seeding rate. Common in roadside mixes, annual ryegrass is important on sites with a severe grade, where its rapid establishment will firmly and quickly anchor the soil and help preserve the site's integrity. Unfortunately, this same aggressive quality can crowd out the perennial grasses the annual ryegrass was intended to aid, particularly if you've added too much annual-ryegrass seed to the mix. For mixes containing slow-growing fine fescues or wildflowers, add no more than 10 percent annual ryegrass (by weight) to the mix, and then only if absolutely necessary to prevent severe erosion.
In northern temperate climates, plant annual ryegrass in late spring (to establish a site during the summer months when other grasses may not persist) or later in the growing season to stabilize a site before winter. Typically, annual ryegrass produces seed and completes its life cycle in the same year it is established. However, fall-planted annual ryegrass may act as a winter annual if the winter season is mild or if the plants have protection from extreme cold. Then it will produce seed the following year. In southern climates, too, you can sow annual ryegrass in late summer or early fall to help stabilize a site and prevent erosion.
* Cereal grains. Annual cereal grains such as cereal rye, barley and oats serve as alternatives for temporary soil-stabilization covers. You can sow any of them alone or in a mix of grains, grasses or legumes. Cereal rye (Secale cereale), or winter rye, is one of the best grains to use as a winter-annual cover crop for projects that extend well beyond typical seeding dates. It germinates and establishes at lower soil temperatures than other grains and grasses. Planting cereal rye from late September to early October in northern locations and late October in southern climates will provide some winter cover and early spring growth.
Cereal rye also is a good companion crop to seed along with native grasses in landscape and golf-course designs. Because germination and establishment of native grasses is slow during the first growing season, cereal rye added to the native-grass mix helps reduce soil erosion while the natives develop their root systems and become established. Many natives such as Indiangrass and the bluestems are warm-season grasses and their use in temperate climates requires longer establishment times than in warmer climates. The cereal rye also helps stabilize the site during winter months, does not crowd seedlings during their establishment and does not persist once active spring growth begins the following year.
* Barley (Hordeum vulgare) tolerates warm, dry conditions although you can sow it in mild-spring or -fall climates as either a summer or winter cover. Site managers usually use barley as a spring planting in temperate climates, while fall- or winter-cover planting is its more common use in the warmer climates of California or the South.
* Oats (Avena sativa) fit well into many reclamation projects for short-term needs. Oats are best adapted to temperate climates and prefer moderate precipitation. This species tolerates a wide range of soil types, provided soil fertility is adequate. Sow oats as a fall crop in southern regions to enhance soil stabilization.
* Sudangrass. Sudangrass (Sorghum sudanense) was first introduced from Africa to the United States in the early 1900s. Sudangrass is a warm-season annual that prefers warm, moist soils but can adapt to a variety of conditions. Used as a temporary green-manure crop, Sudangrass is a common ingredient of pasture or silage crops and reclamation mixes. It can tolerate some moisture stress, which makes it a desirable component in reclamation mixes. Although active growth slows during times of limited moisture, it easily resumes when moisture again becomes available.
* Millet. Millet is an important crop for the forage and birdseed industries and is also useful in soil-stabilization and reclamation mixes. Foxtail millet (Setaria italica), brown-top millet (Panicum ramosum) and Japanese millet (Echinochloa frumentacea) are important temporary cover crops, particularly in the central and southern portions of the United States. Brown-top millet is popular in southern regions for use in damp reclamation mixes. With growing requirements similar to Sudangrass, reclamation mixes often contain millets in addition to, or as a substitute for, that species. Foxtail millet is an annual warm-season grass that matures in 75 to 90 days and requires warm temperatures and ample moisture for optimal growth. Although it prefers warm weather, it has a shallow root system and is subject to drought injury. It has a rather dense, bristly seed head that, when mature, encourages and attracts bird populations.
* Buckwheat. Common buckwheat (Fagopyrum esculentum) is a bushy, squat annual that reaches a height of 2 to 5 feet when fully mature. Nursery-stock producers use buckwheat as a temporary green-manure crop from mid-spring to early July after spring digging and before they line out and replant new fields. Buckwheat can grow between 45 and 105F, with 80F being the optimum. Plant it and allow it to grow at least 12 weeks before the onset of frost.
Perennial grasses Perennial grasses can function as temporary covers before seeding a desired permanent turf. Most perennial grasses have extensive root systems able to tolerate droughty, infertile soils, making them adaptable in disturbed sites.
* Tall fescue. Tall fescue (Festuca arundinacea) is an important cool-season turfgrass used extensively in temporary conservation mixes. A perennial, tufted bunchgrass, this species exhibits an extensive root system and the ability to establish quickly. The deep root system of tall fescue enables persistence in both wet and dry soils. By the 1940s, the USDA Soil Conservation Service recognized the versatility and benefit of the season-long growth of tall fescue, thus making it a more frequent component of conservation mixes. Tall fescue prefers warm soils for establishment and can continue growth when other cool-season grasses have slowed their activity. This makes it a nice addition to conservation mixes designed for both transitional and temperate regions of the United States. In warmer climates, it serves as a fall-seeded cover or as an overseeding grass while the permanent turf is dormant. In the North, tall fescue provides relatively good root growth in droughty, infertile soils such as roadsides and r eclamation mixes. However, its perennial qualities may be a disadvantage in certain circumstances, leading to its dominance of some conservation mixes.
* Perennial ryegrass. Perennial ryegrass (Lolium perenne) is a bunch-type grass significant to the southern overseeding markets. As a quick-establishing temporary cover, perennial ryegrass, whether a common or improved turf-type variety, provides a green surface on which athletic and recreational activities can continue when the permanent turf is dormant. As a temporary grass, it protects dormant warm-season turf and supports recovery and recuperation from wear. In northern climates, its perennial nature and aggressiveness make it undesirable as a temporary cover unless you intend to till the site before seeding with the permanent crop.
When you determine that you need to use a cover crop, your first priority is to select a crop that solves the immediate soil-erosion problem. A consideration of other, secondary needs and factors should lead your final selection of a species or mix of species. What is most important to the site? Erosion control only? Aesthetics? Preservation of bird and animal habitat? Consider the desired effect of the cover crop on the surrounding environment to determine the best selection. Also, consider the effects of cover crops on establishment of the permanent crop you intend to use.
Finally, remember that this article only discusses grasses. Many other excellent, non-grass cover crops are available, especially legumes. Consult a local distributor. Often, suppliers stock seed mixes designed for specific uses in particular regions or climates.
Victoria Wallace is a technical agronomist with Lofts Seed (Winston-Salem, N.C.) and current president of the Rhode Island Nursery and Landscape Association.
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