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Those pretty flowers by the side of the road: Birdsfoot trefoil

 Craig Shaeffer, Agronomy Professor, Jared Goplen, Extension educator-crops, Troy Salzer, Extension educator, Roger Becker, Extension weed scientist, and Nancy Ehlke, Agronomy Professor

Figure 1. Roadside revegetation with a mixture
of birdsfoot trefoil and cool season perennial
grasses.
Among the dried grasses on roadsides and pastures during this past summer’s drought, the eye-catching bright yellow flowers of birdsfoot trefoil (BTF) emerged (Figure 1). Though its use as a forage has declined, birdsfoot trefoil can still make significant contributions in a grazing system. In addition to its high forage quality, the legume can supply nitrogen to grasses in the mixture and together they stabilize the soil, reducing wind and water erosion.

Identification and growth habit

Figure 2. A close-up of birdsfoot trefoil
inflorescence in a group of 4-8 flowers. Note
the elongated seed pods that resemble a bird's foot.
Birdsfoot trefoil has clusters of 4-8 flowers that are arranged in an umbel (think umbrella) inflorescence. Birdsfoot trefoil gets its name from the 1-inch long seed pods that radiate from the flower stem like the toes of a bird’s foot (Figure 2). "Trefoil" means three leaves, although birdsfoot trefoil has a total of five leaflets with two smaller leaflets hugging the base of the petiole. 

Each of the brown seed pods contains 10-15 seeds. Birdsfoot trefoil can flower throughout the season and is able to produce as much as 1000 lbs of seed per acre. The seed is very small and can survive for several years in the soil. This allows for natural reseeding and contributes to its long-term stand persistence.

Birdsfoot trefoil is a short-lived perennial legume with a fibrous tap root that can reach a depth of 24 inches. While not as drought tolerant as alfalfa, its ability to scavenge soil moisture exceeds most perennial grasses that have shallower roots. Compared to grasses, it grows well under low soil nitrogen (N) conditions because it can fix its own N (average of 50-130 lb/acre/year) through biological nitrogen fixation. In addition to providing its own N for growth, birdsfoot trefoil can transfer up to 30 lb N/acre to nearby grasses.

History

Birdsfoot trefoil was promoted as a forage legume from the 1950’s to the 1990’s and was used for soil conservation projects, including roadside revegetation. Seed production was an important industry in northern Minnesota from the 1980’s until the 2000’s. This area supplied the entire market, even though seed was produced on only 3,000 acres. Because of challenges with establishment and its lower yield compared to alfalfa, its use and acreage as a forage has also declined. The most recent birdsfoot trefoil variety evaluation was conducted by the University of Minnesota in 2012. Varieties included Norcen, Pardee, and Empire with yields in pure stands averaging from 4 to 5 ton/acre.

Advantages of BTF in a pasture mix

Birdsfoot trefoil can still contribute to forage productivity on Minnesota farms. It is an excellent grazing legume because of its high forage quality, non-bloating trait, and capacity to reseed. In addition, it is more tolerant of low soil pH and wetter soils than other legumes and has lower P and K requirements than alfalfa does. Birdsfoot trefoil’s yield and carrying capacity are less than alfalfa's, but it can provide higher average daily cattle gains (Table 1). Birdsfoot trefoil forage quality at flowering and later stages of maturity is greater than for alfalfa, which allows for a wider harvest window.

Table 1. Carrying capacity and heifer performance during grazing of three legume species during two seasons.
Legume Carrying capacity Daily gain Seasonal gain
days/acre pounds pounds/acre
Alfalfa 233 (100)* 1.5 (100) 349 (100)
Birdsfoot trefoil 215 (92) 1.8 (121) 387 (111)
Cicer milkvetch 269 (112) 0.9 (63) 251 (72)

*Values in parentheses are expressed as a percentage of alfalfa.

Source:Marten et al., 1987 Crop Sci. 27:138-145.

Condensed tannins

Birdsfoot trefoil is unique in that it contains condensed tannins that provide multiple benefits to ruminants. Condensed tannins are polyphenolic compounds in foliage and flowers that are not directly involved in physiological functions. When ingested by ruminants, condensed tannins interact with proteins to prevent the foaming associated with frothy legume bloat. In addition, they can bind with proteins, reducing their breakdown in the rumen. This creates by-pass protein that allows for increased digestion of essential amino acids in the intestine. Condensed tannins can also reduce methane production by ruminants thus providing opportunities to reduce greenhouse gas emissions as well as reducing volatilization of ammonia from urine. At high enough concentrations, condensed tannins have been shown to reduce gastrointestinal parasites in sheep and goats.

Establishment

Birdsfoot trefoil should be grown in mixture with a noncompetitive grass to minimize weed invasion and to increase harvestability by supporting stems that lodge. Birdsfsoot trefoil seed is small (375,000 seeds/lb) so a seeding rate of 7 lb/acre should be used in mixtures. Seeding rates for timothy, and tall fescue or meadow fescue in binary mixtures should be 2, 3.5, and 4 lb/acre, respectively. In some areas, reed canarygrass (at 3 lb/acre) might be a good fit to include in mixtures with birdsfoot trefoil because they have similar seedling vigor. In addition, the recurring upright growth habit of reed canarygrass aids harvestability during the growing season. Birdsfoot trefoil can also be included in more complex mixtures with a diversity of clovers and grasses. A diverse mixture helps ensure with the goal to thrive in unique soil conditions within a pasture.

Pasture renovations and direct seeding are the most relevant establishment methods for birdsfoot trefoil:

Pasture renovations

Birdsfoot trefoil can be used to renovate existing pastures using sod-seeding or frost seeding. With sod seeding, a no till drill is used to drill seed in the spring following suppression of the existing grass with herbicides. With frost seeding, seed is broadcast on the soil surface in late winter allowing freezing and thawing actions to cover the seed.

In both scenarios, it is beneficial to apply a high stocking rate in the fall before spring seeding to suppress the grass, reduce grass residue, and increase soil exposure. Additionally, grass regrowth should be suppressed by grazing the spring following seeding to allow birdsfoot trefoil seedlings to access light and moisture. Sod-seeding is the most reliable approach to use because it can reliably provide soil-seed contact; frost seeding is riskier because of the dependence on freezing and thawing weather conditions to bury the seed.

Direct seeding

Birdsfoot trefoil can also be established using traditional tillage approaches using companion crops and/or herbicides. The greatest success with establishment of birdsfoot trefoil-grass mixtures occurs in the late summer before 1 September when competition with weeds is reduced and rainfall and temperature are conducive to legume growth. These are described at https://extension.umn.edu/forages/planting-forages. It is critical to emphasize that because of its small seed size, birdsfoot trefoil should be seeded ¼ inch deep into a firm seedbed to insure soil-seed contact. Seed should be inoculated with the appropriate strain of Rhizobium to ensure nodulation and nitrogen fixation.

Management

Birdsfoot trefoil is best used in rotational grazing systems where pastures can be managed. Its persistence and yield are greatest when grazed at flowering and by adjusting the grazing pressure to leave a 4-inch stubble. This allows 3-4 grazings per year depending on the region. Birdsfoot trefoil can also be used in stockpiled grazing systems where forage is accumulated in the field to provide feed during periods of forage deficits. For example, forage can be accumulated in the spring until midsummer or from late summer until fall. Natural reseeding is important for long-term persistence. This can be accomplished by rotational grazing with low stocking rates that does not remove all stems and seeds or by stockpiling a stand at some point in the grazing season at least once every 2-3 years.

Invasiveness

Minnesota DNR includes birdsfoot trefoil in their list of plants that can become invasive in natural areas, due to its potential to suppress native vegetation in restored prairies and roadsides. It was assessed by the MDA Noxious Weed Advisory Committee in 2015 with the recommendation to not regulate birdsfoot trefoil and to allow its continued use in agricultural grazing systems. It is recommended however, that birdsfoot trefoil not be established adjacent to natural or restored prairies.

Sources of information


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