Benefits of Legume-Grass Mixtures

By Craig Sheaffer and Jared Goplen

The most compelling reasons to use mixtures containing both legumes and grasses are related to the benefits of plant diversity on sward productivity, yield persistence, and livestock nutrition.

An alfalfa-meadow fescue mixture. Meadow fescue
is a relatively new grass in MN, with good
persistance and high fiber digestibility.
Source: J.H. Cherney, Cornell University

Advantages of a forage mixture

Legumes and grasses have unique herbage and root morphology traits that allow for a greater combined use of environmental resources such as light, moisture and minerals. However, legumes and grasses should be selected for mixtures with similar adaptation to harvest regimes and environmental conditions. Here are some agronomic benefits:

• Legumes have unique root systems. Nodules on legume roots are able to fix N from the air for their own nutrition and can transfer up to 50 lb/acre to grasses growing in association. Because of their tap roots, some legumes like alfalfa are able to absorb water from deeper in the soil than grasses, and therefore have greater drought tolerance than grasses.
• Winterhardy grasses have broad crowns. Grasses grown in mixture with tap rooted legumes like alfalfa provide protection for legumes from winter injury associated with heaving of soils. Grasses also are more traffic tolerant than legumes and can protect legume crowns from wheel traffic.
• Winterhardy grasses have greater tolerance of environmental stress than legumes and even some grasses like ryegrass. Growing winterhardy grasses with legumes can provides greater overall stand persistence and yield if one or more of the mixture components should die.
• Faster field drying times. Grasses typically contain less moisture than forages which reduces field drying times.

From a livestock nutrition standpoint, grasses can contribute to rations: 

• Grasses contain more highly digestible fiber than legumes.
• Grasses have lower levels of non-fiber carbohydrates (NFC) (15%) than alfalfa (25%) and corn silage (35%).
• Grasses reduce the risk of frothy legume bloat in cattle and sheep grazing clovers and alfalfa (when ≥40% of the stand).
• Immature grasses can increase the overall palatability of mixtures

How much grass should be in the sward?

To provide both agronomic as well as ruminant nutrition advantages, a minimum of 30-40% grass should be in mixture with legumes in a sward. However, the ideal level of grass may vary depending on the use of forage in grazing and livestock feeding. When feeding dairy cows at the peak of production with high protein and energy needs, a grass composition as low as 20% may be desirable. As much as 40-60% grass is likely desirable for grazing beef cows and calves. Therefore it is important to test forages for nutrient composition when using legume/grass mixtures in cattle rations.

While we can establish target composition goals it is important to recognize that the legume – grass proportion is affected by the time of seeding and will vary both within a season and over the life of the stand.

Figure 1. Alfalfa-grass and alfalfa forage yields for 3 years after seeding in central MN. (Peterson et.al., 2010-2012. MFA reports)

• Grasses will establish better with early spring and later summer seeding, and without competition from weedy grasses and grass companion crops. In much of Minnesota the best time for grass establishment is in late summer but before 1 September.
• Grass proportion in mixtures will typically be highest in the spring and fall when temperature and moisture availability are best. Cool season grasses undergo a summer slump and have lower yields from late June through September.
• Grass proportion in mixtures often increases with increased stand life because legumes are less persistent than grasses (Figure 1)

How to determine sward composition?

Sward composition can be determined visually and by hand separation of subsamples. Visual determination of legume-grass mixture swards can be challenging but are quite accurate with experience. The challenge in visual estimation of composition occurs because typically we only look at the top of the canopy, but adjustments need to be made to compensate for what is hidden within the canopy. Hand separation of subsamples taken following visual observation can be very accurate as long as at least 10 – square foot and representative samples are taken across a field. The sample can be separated into grass-legume components by hand and then weighed.

Simple mixtures

Simple mixtures should contain at least one legume and a grass that are compatible in terms of tolerance to harvest management and environmental conditions. The proportion of each in the mixture will depend on livestock fed and use for grazing or haying. For these mixtures, orchardgrass, tall fescue, and meadow fescue are recommended to be seeded individually at rates of 4, 6, and 6 lb/acre respectively, to provide 30-40% grass in mixtures. These grasses have similar yield potential but meadow fescue has somewhat higher forage fiber digestibility. They all have stem elongation and flower only in the spring and are only leaves at later harvests during the year. Orchardgrass and tall fescue can compete with and crowd-out alfalfa as stands age (Table 1). Varieties of all grasses should be selected that “head out” or mature later than alfalfa flowers to reduce the fibrous stems in the forage and not reduce quality.

Table 1. Steer gain while rotationally grazing alfalfa-grass mixtures in Wisconsin. Results are from a 3-year old stand. Differences in average daily gain were associated with greater proportion of alfalfa in the alfalfa-meadow fescue mixture. The authors concluded that meadow fescue was more compatible with alfalfa and provided a better grass:legume balance. Source Nieman et al., 2019 Agron J. 11:686.

Timothy and smooth brome grasses are no longer recommended for mixtures with alfalfa because these grasses will not persist in an aggressive, three- or four-time harvest regime typically used in alfalfa growing regions of Minnesota. Timothy and smooth bromegrass perform best in a two-cut harvest regime. Timothy is adapted to mixtures with birdsfoot trefoil grown on low pH or wet soils.

Complex mixtures

Complex mixtures contain two or more legumes and grasses that provide unique contributions to the mixture in terms of adaptability to environmental condition, management, or livestock nutrition. An example of a complex mixture intended for beef cattle grazing is shown in Table 2. Some comments about the mixture:

• This mixture will produce a sward that is predominately grasses based on seeds (60:40) with about equal proportions of orchardgrass, tall fescue, and meadow fescue. Variety names are not provided but all grasses have been selected for high quality. The orchardgrass is late maturity, and the tall fescue has soft leaves for greater palatability and is endophyte free (endophytes produce alkaloids in tall fescue that reduce palatability). Meadow fescue is high in fiber digestibility. All of the grasses persist well if rotationally grazed from 4-5 times per year.
• Perennial ryegrass is included for its high seedling vigor, quick ground cover and high forage quality, but it lacks winterhardiness and will not provide long-term persistence.
• Alfalfa varieties are grazing tolerant and should be compatible with grasses. The creeping rooted type alfalfa has potential to spread and reduce late winter “heaving”, but has less yield potential than standard alfalfa varieties.
• A small amount of red clover and birdsfoot trefoil are included to increase legume diversity. Red clover has greater seedling vigor than alfalfa and will likely provide some yield enhancement during the first year of production. Birdsfoot trefoil, a tannin-containing legume, has potential to reduce bloat and increase protein by-pass, but its low seedling vigor might limit its establishment except in areas where there is little competition.

Table 2. An example of a complex mixture developed for beef grazing in western Minnesota. The mixture was intended for seeding in mid-August at a rate of 20 pounds per acre.

Note: This mixture contains about 60% grass seeds and 40% legume seeds. 75 seeds per sq. ft are normally adequate for establishment of stands under good conditions including good soil seed contact and seeding at 1/4 inch. Therefore, about 10 lb per acre of this mixture should be adequate under ideal conditions, but it was seeded at 20 lb per acre to provide greater assurance of successful establishment.

Conclusions

Legume-grass mixtures have potential to provide agronomic and livestock feeding benefits. Mixtures containing 30-40% grasses are typically recommended, but the exact proportion is affected by seeding date, stand age, and harvest scheduling. Both simple and complex mixtures have advantages depending on livestock feeding and agronomic goals. Legume and grass components of mixtures should be selected based on adaptation to harvest regimes and prevailing environmental conditions. Orchardgrass, tall fescue, and meadow fescue have the best compatibility with modern alfalfa harvest systems and rotational grazing, but varieties of these grasses should be selected to match their use in haymaking and grazing systems.