cows in field

Companion Grasses for Forage Legumes

By Allen Wilder, Forage Agronomist, the William H. Miner Agricultural Research Institute, Chazy, NY and Sid Bosworth, Forage Agronomist, retired, University of Vermont Extension

Picture4_thumbGrasses are amazing organisms. This diverse family of plants is one of the most abundant and its members can be seen in nearly every inhabitable corner of the earth. Some grasses can tolerate flooding or even grow in standing water, while others can go for months on end with barely a drop of rain. It is not surprising then, that many of our most productive crops (such as corn, rice, and sugar cane) are grasses. In the case of ruminant agriculture, almost all cool-season grasses can become a valuable crop if managed properly. That is one reason why cool-season grasses are an excellent companion to forage legumes.

We know that forage legumes are an important part of organic forage systems. Recent NODPA articles by University of New Hampshire (UNH) researchers have highlighted the numerous nutritional and agronomic benefits that forage legumes provide (Brito et al., 2020; Smith and Warren, 2020). While legumes often have exceptional nutritional quality and are capable of fixing their own nitrogen fertilizer, they can be difficult to maintain in monocultures. This is because forage legumes are susceptible to numerous stresses involving soil conditions, pests and diseases, and winter injury. That is why most forage legumes seeded in the Northeast are planted as a mixture with one or more cool-season grasses.

What to look for when selecting a companion grass

The role of a companion grass in a legume stand is to complement the characteristics of the legume in such a way that an efficient symbiosis is formed. This means that the species should compete with each other as little as possible when growing as a plant community. A highly competitive companion grass, such as tall fescue, should not be used with a poorly competitive legume, such as birdsfoot trefoil, if the legume population is expected to endure. Companion grasses should also be chosen so that they add resilience to the sward. If the legume is prone to winter injury, then it should be combined with a very hardy grass. Additionally, some species of grasses and legumes can spread vegetatively (e.g. white clover, reed canarygrass, and bromegrass), while others cannot (e.g. alfalfa, orchardgrass, and tall fescue). If a companion grass is being chosen for a non-spreading legume, then using a spreading companion grass will allow the grass to fill in any empty areas should legume populations decline.

Forage quality is another factor that should be considered when choosing a companion grass. There are species and varietal differences in maturity and forage quality that could make a difference in the overall quality of harvested forage. In comparison to grasses, forage legumes are high in protein and low in fiber content. Therefore, the easiest way to ensure high-quality forage may be to maintain a high legume proportion. However, while legume fiber is digested rapidly, the overall digestibility of legume fiber is lower than that of cool season grass fiber. As seen in Figure 1, the fiber digestibility of an organically managed legume sward increases as the companion grass proportion increases. This means that if poor legume digestibility is limiting intake, then a high-quality companion grass may make a big difference. Ideally, the companion grass reaches optimal maturity at the same time as the legume. This is difficult to achieve in practice, however since legume and grass maturity gaps differ from year to year. Grass cultivars should be selected based on regional variety trials since heading date and forage quality differences are likely location dependent.

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Companion grass research at the University of Vermont

In collaboration with UNH, a small-plot study was established at a University of Vermont farm to compare four companion grass species in combination with one of three forage legumes. Alfalfa, red clover, and birdsfoot trefoil were the legumes used in this study and each was planted with timothy, tall fescue, meadow fescue, or perennial ryegrass. Legumes were also planted in monoculture for comparison purposes. Additionally, two cutting management strategies were used with a cutting height of approximately four inches. One cutting management was designed to mimic a typical four cut system that might be used by a farm seeking to maximize forage quality. The second management strategy simulated a delayed cutting strategy with only three cuts per season. Data was collected on sward yield, composition, and quality for two production years and analyzed using an analysis of covariance (ANCOVA) model.

Although the companion grass generally contributed less than a quarter of the total dry matter yield (averaging 23.6% across harvests and years) the companion grass species did influence the total seasonal yield of the legume stand (Figure 2). Legume stands with timothy as a companion grass had significantly higher total dry matter yields than stands with the other companion grasses. Conversely, legume stands that were seeded with perennial ryegrass yielded significantly less dry matter at the end of the season. Interestingly, higher forage quality was observed when perennial ryegrass was used in some cases, but this did not outweigh the yield drag when predicted milk production was estimated on a land basis (Figure 3).

When we looked at legume stands with differing grass treatments under intensive and delayed cutting management, we found that potential fiber digestibility (240 hours) was dependent on both cutting management and grass species (Figure 4). It appears that meadow fescue was well suited for intensively managed legume stands but might be a poor choice if the cutting schedule is delayed. Timothy, on the other hand, proved to be well suited to the delayed cutting management system since fiber digestibility did not change very much when the harvest schedule was delayed. Thus, using timothy as a companion grass could allow for greater harvest flexibility and maximize total dry matter yields. We observed that timothy was highly aggressive at first cut but backed off during aftermath cuts allowing the legume to take advantage of the summer heat. Timothy is also very tolerant of the cool and moist conditions that occur when we have a wet spring (unlike some legumes).

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Take home message

Adding a companion grass to forage legume seedings can be a great risk mitigation strategy for organic farms. Care should be taken, however, to select a well-adapted species and cultivar that will complement the characteristics of the legume. Research from the University of Vermont demonstrates that companion grass choice can impact forage yield and quality even if the companion grass makes up a relatively small portion of the sward. Timothy promoted the highest yields when used as a companion and was well matched with most legumes. Perennial ryegrass may occasionally boost forage quality when used as a companion grass but could depress yields through competition. Keep in mind that these data come from a relatively short study and a single location. Also, only one variety of each grass species could be evaluated. Informed decisions should be made about companion grasses based on local agronomic recommendations and on-farm experimentation.

Bibliography cited

Brito, A.F., Lange, M.J., and Silva, L.H.P. 2020. The key role of forage legumes in organic dairy diets: effects on your bottom line. NODPA News. Available at: /n/945/The-Key-Role-of-Forage-Legumes-in-Organic-Dairy-Diets-Effects-on-Your-Bottom-Line

Smith, R.D., and Warren, N.D. 2020. Managing forage legumes for improved oroductivity and persistence. NODPA News. Available at: /n/1951/Managing-Forage-Legumes-for-Improved-Productivity-and-Persistence

Allen Wilder, M.S., is a Forage Agronomist at the William H. Miner Agricultural Research Institute, Chazy, NY 12921. He was formerly a graduate student at the University of Vermont in the Department of Plant and Soil Science. He can be reached at: office phone (518) 846-7121 Ext. 144; email Sid Bosworth, Ph.D., is a recently retired University of Vermont Extension Forage Agronomist.

Posted: to Organic Production on Mon, Sep 28, 2020
Updated: Mon, Sep 28, 2020