Those in the cattle industry have come to understand the term “hybrid vigor” and how it benefits the health, growth and stamina of our livestock. Many of the same things can be said for our pastures. Mixed pastures, or pastures interseeded with legumes, can be more productive and can fill more needs of our soil and livestock than a monoculture grass pasture. Adding legumes can provide additional nitrogen for the forage in that area and provide better nutrition for the livestock grazing it.
With nitrogen being one of the most limiting nutrients in the plant growth cycle, any additional source of nitrogen is a welcome benefit to pasture production. Legumes have the capability to take raw nitrogen from the air or soil and convert it into a usable form for plants. Legumes do this through a symbiotic (mutually beneficial) relationship with rhizobia bacteria. It is this bacterium that performs the actual work to convert this nitrogen to a usable form. In return, the plant provides some carbohydrates, which the bacterium needs for survival. This relationship creates an environment with more nitrogen available to not only the legume plants themselves but also the surrounding plants in that area.
This process of nitrogen fixation adds a natural source of nitrogen – as opposed to applying fertilizer containing nitrogen. Studies have shown that adding legume/grass pasture stands can have similar levels of nitrogen acquired from symbiotic sources as a legume-only stand. These levels of added nitrogen can help to make production nearly equivalent to that of commercially fertilized pastures. A team of researchers in 2019 found that tall fescue pastures with either added birdsfoot trefoil or alfalfa had similar, if not equal, amounts of herbage available to animals when compared to monoculture tall fescue pastures fertilized with nitrogen. This research demonstrates that nitrogen fertilizer applications could be greatly reduced or nearly eliminated from pastures that have a nitrogen-fixing legume interseeded in them. This would aid the productivity and profitability of nearly any pasture.
Not only do we have an added benefit from the viewpoint of plant productivity and decreased fertilizer usage, but legume/grass mixed pastures also provide added nutritional value to the livestock that graze this forage. Legumes are known for containing higher levels of crude protein (CP). Levels of CP in perennial legumes will be anywhere from 23% to 30% of dry matter in the vegetative stage to 17% to 20% of dry matter in the early bloom stage. In comparison, perennial cool-season grasses such as orchardgrass, smooth bromegrass and tall fescue can have CP levels of only 20% to 26% of dry matter in the vegetative stage to 11% to 13% of dry matter in the heading stage. These higher levels of CP being available to grazing livestock, along with higher digestibility and lower fiber values, lend themselves to being a forage that can meet nutritional needs for improved performance better than a monoculture grass pasture. This higher digestibility is one of the reasons why grazing animals can consume more pounds of dry matter in a mixed pasture as opposed to a monoculture grass pasture and therefore have higher rates of gain.
Some legumes that one may choose to add to an existing (or new) pasture could include alfalfa, clover, sanfoin, clovers, cicer milkvetch and birdsfoot trefoil. Each one has different qualities that allow selection for those better adapted for a specific area or condition. It is recommended to have a conversation with your local seed provider to see what grasses and legumes work best in your area. Despite all the positives of adding legumes into pastures, many legumes do come with a downside. The rapid breakdown of these highly digestible proteins in legumes creates a froth or foam to form over the top of the rumen contents. This foam reduces and eventually eliminates a ruminant’s ability to belch excess gas from its rumen. This leads to rumen distension (bloat), and if left untreated, it can eventually lead to death. However, some legumes are less likely to lead to this frothy bloat. A select few, such as birdsfoot trefoil, sanfoin or cicer milkvetch, are considered nonbloating legumes. These plants contain condensed tannins (CT), which are naturally occurring compounds. The CT will create insoluble complexes with proteins and as a result, are unable to be digested in the rumen. The acidic environment of the abomasum causes these insoluble complexes to be broken up, rendering these proteins available to the animal in the small intestine. These three specific legumes can be added to pastures to reduce bloat concerns. If you have an existing pasture with a different legume in it that may be a cause for concern, there are ways to prevent that bloat.
- Establish and manage pastures so that alfalfa and clover make up less than 50% of the forage biomass.
- Allow animals to fill on dry roughage before turning out on bloat-prone pastures.
- When grazing a bloat-prone pasture, feed dry hay or windrow graze.
- If legumes make up more than 50% of the forage biomass, feed antifoaming agents, such as poloxalene, in a molasses-containing block. Also, consider moving animals to a drylot or other area following heavy dew or rain to reduce chances of bloat.
- Consult with your veterinarian and plan ahead to be competent in handling a severe bloat event.
If you are considering planting legumes into your pasture, there are a few ways to go about it. Prior to seeding the legume species you have chosen, it is recommended that you lightly till or heavily graze/mow the soil you plan to incorporate your legume into. This will help your new legume to take a foothold in the soil with less competition from the grass. Planting in the summertime when the cool-season grasses are not as productive will also help this. After your preparation, you may proceed as simply as broadcasting seed onto your existing pasture and then running a harrow over the top to improve seed-to-soil contact. With this method, you should plan for a higher seeding rate than recommended to ensure that a sufficient number of seeds make contact with the soil to begin growing. No-till drills are a versatile option when planting legumes and do a great job of not disturbing your existing pasture to a large degree. These are becoming a more common implement and are typically available for rent from local equipment stores, the NRCS or soil and water conservation districts in your area.
For more information on the topic of legumes and integrating them into a grazing program, both the Idaho Forage Handbook and Pasture and Grazing Management in the Northwest are great resources that provide valuable knowledge about pasture management and how to properly manage legumes in those pastures.
So if you have been putting some thought into how you are going to make your pastures more productive this year, consider adding legumes. The increased fixed nitrogen, greater herbage mass, improved CP content, better digestibility and greater ability to meet nutritional needs make adding these versatile forages to your existing pasture grass an option worth considering. It isn’t perfect and may require some preventative measures for bloat, but it is still a great option for adding that boost to your yearly grazing plan.
References omitted but are available upon request by sending an email to an editor.
