Forage Legume Establishment and Maintenance

Two opposite conditions are often faced when establishing forage legumes. They are clean-tilled seedbeds normally associated with alfalfa production and no-till seedbeds normally used when adding forage legumes to an existing grass meadow. Some guidelines are appropriate for one of these and not the other.

Site Selection - Choose a deep, fertile, well-drained soil for high yield. Forage legumes can be productive on sites that are less than ideal, but yield and/or persistence will be generally less on less-than-ideal sites.

• If hay production is important in addition to grazing, the site should be smooth and level enough to safely operate haying equipment and hauling vehicles.
• Shallow soils can be used successfully for forage legumes production; however, adjustments (reductions) should be made to estimated forage production when developing forage budgets.
• Most forage legumes are not as productive as grasses in poorly-drained sites, and perennials tend to be short lived. In such cases reseeding every year or two becomes important. Prior to sowing forage legumes, if possible, drainage should be improved, when using sites with poor surface drainage.

Soil Test - Apply fertilizer and lime according to a reliable soil analysis.

• Forage legumes seldom need applied nitrogen fertilizer; however, they tend to require higher concentration of phosphorus and potassium than grasses. Forage legumes seldom reach their productive potential if soil pH is below 5.8. Agricultural lime should be applied to neutralize acid soils, and fertilizer should be utilized to supply phosphorus and potassium when the soil is deficient.
• Lime and fertilizer can be effective when applied to the soil surface for forage legumes; however, incorporating into the top 3 to 6 inches of soil prior to planting allows more efficient use of fertilizer and quicker action of lime.

Land Preparation - Plow, level, and drain low areas, well before sowing, if legumes are sown in clean-tilled areas. When sowing legumes no-till into grass, the grass should be grazed or mowed short prior to planting. It is important to have good seed-soil contact, and deep thatch and standing grass hinder seed-soil contact. Standing grass and thatch more than 4 inches high shade seedlings and reduce early growth.

Seedbed Refinement - Develop a level, mellow, firm bed with small clods for clean-tilled sites.

• This will improve seed-soil contact and assure that rain enters the soils and remains available for seed germination and seedling development.

Species and Variety Choice - Select adapted species and varieties.

• Except for alfalfa, varieties seem to impact yield and persistence very little.
• A mixture of aggressive, resilient types is usually more important than the choice of any individual variety. Perennial species should have the ability to persist for several years in the particular environment and grazing management system. Annuals must produce seed annually to assure an adequate supply of seed in the soil.

Seed Quality - A small amount saved by buying "cheap" seed may cost greatly in a poor stand established.

• Read labels on seed sacks to determine percent germination, weed seed, foreign material, and date tested.

Planting Date - Sow during August 25 to September 25 or March 15 to April 15 in Oklahoma.

• Most perennial legumes can be successfully established in fall or spring.
• Cool-season annual legumes should be planted early enough in late summer to produce several leaves (and a good root system) prior to the onset of severe winter temperatures.
• Warm-season annual legumes should be planted soon after the risk of severely cold temperatures (below 10⁰F) is below 50% so that they can become well-established prior to the onset of likely high temperatures (above 85⁰F).

Seed Placement - Press seeds and cover with 1/4 to 1/2" soil for small seeded legumes. Do not bury seeds to a depth more than 10 times the diameter of the seed.

• Seeds buried too deeply, on the soil surface, or on top of thatch seldom develop into vigorous plants.
• Treading in seed with animals can result in good seed placement; however, a high stocking density is required. This means several animals per acre for several days, and the more standing grass and thatch present, the more treading is required. Low stocking density for a long period of time is rarely successful because some seeds germinate and are killed by grazing animals while others are placed in a good germination environment too late in the season for effective establishment.

Sowing Rate - The ideal pounds of seed per acre varies depending upon species and seed size. Generalized sowing rate tables are normally usable as published in various publications (for example OSU Extension Facts F-2585).

• Normally 40 to 50 viable seed per square foot is adequate for a full pure stand. Ten to 20 viable seed per square foot is adequate when adding forage legume seed to established grass. Using seeders that place the seed in a good environment allows the use of fewer seeds per square foot than broadcasting seed on top of standing grass and thick thatch.

Planting Equipment - Calibrate and adjust planters to place seed into a good seedbed.

• Specialized drills that have a box for small seeds and disk openers with depth bands to accurately place the seed 1/4 to 3/4 inch deep normally perform a good job. Packer wheels firm soil over and around seeds.
• Double corrugated roller seeders that drop seeds between the corrugated rollers is good for clean-tilled seedbeds. While these may be considered the best alfalfa seeders for many soils, they leave clean-tilled sandy soils vulnerable to wind erosion.
• Grain drills, equipped with small-seed attachments, can accurately meter small-seeded legume seed. It is difficult, however, to place the seed at the proper depth. If the drill does not have press wheels, rolling or dragging a spike-toothed harrow immediately following planting is advised to help improve seed placement and soil contact.
• Pneumatic seeders, mounted on flotation-wheeled vehicles, can sow fields rapidly and accurately. These work well to distribute seed on established grass or on fluffy, dry, sandy soils that cannot be firmed by rolling. Lightly packing, dragging a chain, or harrowing covers seed.
• Aerial broadcasting is another method used to plant legumes with good success. Because uniform application can be a problem with broadcast planting, two passes in a crossing pattern are often required. After broadcasting, it is advisable to roll fields or drag a spike-toothed harrow to improve seed-soil contact.
• No-till or minimum-tillage drills can do a good job of placing legume seed at the correct depth. When planting on steep slopes or otherwise erosive or shallow soils, it is suggested that minimum tillage be used for seedbed preparation.

Seed Inoculation - Rhizobium inoculation is essential for nitrogen fixation. Use Rhizobium bacteria that is specific for the particular legume or mixture of legumes.

Insect Control - Insects can devastate seedling legumes, underscoring the need to scout fields frequently. Granular insecticides, applied at planting time, may be helpful when grasshoppers or worms are prevalent.

Strategies for Improving Forage Legume Persistence

Forage legumes normally grow with grasses. As a pasture component, forage legumes are the most fragile species in the system, so emphasis should be placed on managing to improve their well-being. Even clean-tilled alfalfa stands, that are thought to be monocultures, grow in association with grasses much of the time. Companion crops (including volunteer wheat) and grassy weeds are nearly always present in new alfalfa stands. The companion crops should be short lived, or they will compete with alfalfa. During later years of an alfalfa stand, weeds (frequently grasses) encroach into spaces left by dead alfalfa plants. Most management strategies to keep alfalfa stands thick are devoted to giving the alfalfa plants an advantage over the grasses.

Knowledge of Plants Helps Manage Them

The term "forage legumes" encompasses many different species, and among the species of important forage legumes, many different combinations of growth types and life cycles are represented. In addition, various varieties within the species react differently to various environmental and management conditions. Because of this wide variation, there is no universal strategy to maintain a healthy, thick vigorous stand of forage legumes. It may help to understand this diversity to think about three contrasting types of forage legumes -- alfalfa, white clover, and hop clover. Alfalfa is a perennial, as is white clover, but hop clover is an annual.

Three Brief Contrast of Forage Legumes

Alfalfa stands may potentially last for a decade or more, but the number of plants per unit area begins decrease shortly after planting. During the first few months and years, larger plants with more stems per plant compensate for the smaller numbers of plants. Eventually larger plant size cannot compensate for fewer plants enough to fully occupy the area. Alfalfa reliably produces seed only in certain environments and management schemes. When alfalfa does produce seed and they fall to the soil, very few new plants result from the seeds, and those plants that do develop are generally a foot or more away from old plants. It is unusual for an alfalfa stand to thicken up, even if seed is drilled into an old stand.

White Clover stands tend to become more dense in many environments even with little seed produced. This is because it reproduces vegetatively by stolons. Individual white clover plants seldom live for more than 2 years, but new daughter plants are produced every time the environment is good. Using this vegetative mechanism of reproduction, well-fertilized white clover pastures (as well as in lawns) can remain thick for many years.

Hop clover is an annual that lives only a few months. With favorable conditions during the last weeks before death, hop clover produces seed that fall to the ground. Many of the seeds are "hard" and will not germinate until the passage of much time. Some of the seeds will germinate at the next appropriate time to establish new plants (early fall). Many of the seeds will remain viable but hard for several years, some breaking dormancy each year. The supply of seed in the soil assures several new stands of hop clover even if they do not produce abundant seed crops each year.

Three Growth Types =
Three Management Targets

The three examples illustrate three groups that have different persistence strategies. Alfalfa belongs to the "crown formers" along with red clover, several species of trefoil, sericea lespedeza (perennial), and cicer milkvetch. White clover belongs to the "clone formers" along with crownvetch, and kura clover. Hop clover belongs to the "reseeders" along with most annual clovers (arrowleaf, berseem, crimson, persian, rose, subterranean, etc.), hairy vetch, annual medics, and annual lespedeza (common and Korean).

• Management of crown formers such as alfalfa emphasizes longevity of individual plants. They need a constant supply of minerals (potassium, phosphorus, calcium), a pH near neutral, a constant supply of water, harvest schedules that allow plants to store essential proteins and carbohydrates in the roots between cuttings, and freedom from disease and insect pests. Individual plants rarely live more than 3 years in red clover, another crown former, so producers normally reseed the stands every 2 to 3 years or allow it to produce seed which will produce new plants.

• Management of clone formers emphasizes the spread by stolen or rhizomes rather than the longevity of individual plants or production of seed for reseeders. Stolons develop more rapidly on vigorous plants, especially if light penetrates through the canopy to stimulate branch development. Vegetative reproduction allows clone formers to expand the species into nearby areas of low competition. Clone formers with prostrate growth and stolons are more tolerant of frequent defoliation than those with upright growth or crown formers. Perennial species with vegetative propagation are able to invade nearby areas with greater certainty than are seed producing species; however, they lack the ability for long-distance dispersal, a strength of reseeders.

• Annual reseeders must re-establish stands each year by producing at least moderately high seed yields frequently enough to maintain a seed bank in the soil. Stand persistence is limited by inconsistent reseeding. If all seeds are "soft" and germinate with the first rain, all seedlings may die during a single poor weather event. Consequently, reseeders must also produce a significant quantity of hard seed. Reseeding annuals are only present for a relatively short period of time each year; therefore, management strategies must be designed to utilize the forage and the allow for seed production.

Harvest Management of Crown Formers: As a consequence of forage legumes belonging to different general groups, the correct management for a species depends on its mode of perennation and expected individual plant longevity. Whether alfalfa is to be harvested as a hay crop or grazed, for long stand persistence it should be harvested a few times a year. After each harvest it should be allowed to regrow and reach flowering stage before it is re-cut. This is the normal way alfalfa is harvested for hay, haylage, or greenchop. If it is to be grazed, it should be rotationally stocked so that all plants are eaten (harvested) during an interval of a few days, then allowed to regrow before grazing again. During a grazing period, the stocking density should be high so that all the forage is consumed (harvested) before regrowth begins.

Harvest Management of Clone Formers: White clover, on the other hand, can withstand close grazing with continuous stocking. Opening up the canopy of plants allows light to the stolons and stimulates their growth. With continuous stocking, the stocking rate should be adjusted to keep the height of grasses short enough to allow light into the white clover stolons, but grazing should high enough to leave some leaves on the clover for continued growth. When white clover is harvested (mechanically or with animals) few stems are harvested because they are close to the ground. Haying or grazing primarily harvests leaves. White clover should not be grazed or cut so close to the soil surface that new stolons are cut. When the management decision is made that white clover should produce seed, harvesting should be deferred until after seed are ripe. Harvesting as hay or by grazing will shatter seed and stands may be thickened.

Harvest Management of Reseeders: Annual reseeders such as hop clover should be cut or grazed after the initial flush of growth in the spring and then defer grazing until after seed set. Arrowleaf clover and hairy vetch have much higher yield potentials than hop clover and should be grazed several times during late spring and allowed to regrow each time in a rotational stocking system. They can also withstand moderate continuous stocking, removing animals in time to produce seed before plants die in the summer. Stocking rate should be high enough on arrowleaf clover and hairy vetch to avoid accumulating excessive growth because most animals do not like to graze rank arrowleaf clover or vetch. Warm-season annual reseeders such as annual lespedeza can be managed with the same general philosophy as cool-season legumes, but the seasons of rapid growth and seed production are several months later.

Mixtures of the different types of forage legumes can be managed; however, more skill is required than when managing for a single type. Mixtures of types have the advantage of buffering against a complete legume failure. When conditions prevail that do not favor growth of one species, it is likely that another in the mix will flourish. In general the harvest (grazing) management style should not completely disfavor any of the mixture which means that none of the species in the mix will have optimum conditions. Compromises normally work well for mixtures of forages in the same field.

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