Why Add Clovers to Pastures?
By: C. P. Bagley, Director
Beef Research Institute
Southern University Ag Center
This will be a series of two articles, the first on why I should add clovers (legumes) to a pasture mixture for grazing livestock. The second article will deal with which clovers are recommended and where they “fit” best in a grazing situation.
While there are lots of grasses grown in Louisiana, the two predominant ones are warm-season (summer) perennials that include bermudagrass and bahiagrass. Both are well-adapted C-4 grasses that can be long-lived, withstand almost any grazing pressure, are highly productive, and grow best under warm temperatures. Generally, these grasses will not grow when nighttime temperatures are 50 degrees and below, and they slow down but do not stop growing under hot temperatures. On the contrast, most of our widely used clovers are termed “cool-season” plants, C-3, and they stop growing when temperatures get hot, but only slow down under cold temperatures.
Adding clovers to your forage mixture has several advantages we will discuss in order:
Clovers “fix” their own nitrogen (N)
Clovers can indirectly contribute N to the companion grasses
Clovers are higher in quality than grasses and produce higher animal performance
Clovers extend the forage growing season and help with Carbon (C) sequestration
Clovers “fix” N: Earth’s atmosphere is 79% N, as N2, so there is no shortage of N, it is just not in a form readily available to plants or animals. Certain bacteria in the ground can form a symbiotic relationship with the roots of a clover plant, with the formation of nodules (infections) on the roots. Bacteria in these nodules capture N2 gas and turn it into NH3 that can form amino acids for the bacteria or in the free form for use by the clover. When cut into, a functioning root nodule will be pink color internally. The “donation” of N from the bacteria on the roots to the plant is in the range of 50 – 100 lb of N per ac (120 – 240 lb/ac of urea fertilizer). The amount of N fixed by bacteria is directly related to the dry matter yield of the clover plants.
Clovers contribute N: The N that is “fixed” in clovers can be made available to companion grasses, but that is not a direct transfer. Rather, the N in clovers is available to the companion grass after cows graze the forage and expel the undigested forage as either urine or feces. When clover plants die, that plant material becomes organic matter in the soil and can break down and yield its N content.
Clovers are higher in quality: Clovers in a forage mixture with bermudagrass or bahiagrass are both higher in quality and have faster digestion rates, both of which increase animal production when grazing clovers.
When several decades ago scientists began to look at forage quality attributes, and correlate those quality characteristics with expected animal performance, they always underestimated animal performance on alfalfa and other legumes. Using alfalfa as an example, since it is a major hay commodity, scientists would measure alfalfa quality attributes and then add the “X” factor to account for the higher rates of animal performance of cattle fed alfalfa hay than what was predicted by the measured forage quality attributes. At that time, no what knew what “X” was, but after some number of years it was explained.
The Lag Phase
When a cow or other ruminant consumes a forage plant, it goes directly into the rumen of the animal where bacteria “attach” themselves to the plant and start to digest it. Animals cannot breakdown cellulose/ fiber themselves; they depend on rumen bacteria to perform that task. The period between when the forage enters the rumen until bacteria attach to the plant and start to digest it is called the “lag phase.” In general, since plant age and other factors affect the length of the lag phase, the lag phase is 2 hours for clovers (including alfalfa), 4 hours for cool-season grasses (ryegrass), and 6 hours for warm-season grasses (bermudagrass and bahiagrass).
So, the “X” factor causing animals to perform better than expected is simply that alfalfa (and other clovers) digests more quickly than grasses do, allowing cows to eat more and take in more energy so they gain faster. Think of a cow’s rumen as a 40-gallon jug. Once it is full, the cow must stop consuming grass due to a lack of space. The faster a forage digests, the quicker the cow can replace it with more forage.
While definitive data has been difficult to come by, most scientists are of the opinion that optimum gains in cattle grazing grass-clover mixture are reached when clovers represent about 25% of the forage mixture. Since most clovers are classified as "cool-season" plants, they usually make up more of the forage mixture in early spring, with summer grasses increasing in summer, which lessens the percentage of clovers in the forage mixture.
Animal grazing habits are quite different. Cows tend to be non-selective and cannot graze much closer than 2 inches above ground level. Sheep, goats, horses, and deer are more selective grazers and tend to choose higher-quality forages and can graze plants all the way down to ground level. Horses graze about 14 hours a day, as they select more favored forages, compared to the 8 hours a cow grazes eating all forages within reach. Since cows tend to graze about 8 hours per day in 3 or 4 grazing periods, there are constant digestive processes going on due to the continual intake of forages by the grazing animal with mixing of the grasses and clovers in the rumen.
Clovers and Carbon Sequestration: There is almost total agreement that carbon dioxide (CO2) levels in the atmosphere have increased from 280 to 410 ppm over the past 100 years due to the burning of coal and petroleum products, generally referred to as “human activity.” Scientists are divided as to the impacts of increased CO2 levels of the supposed “global warming/ climate change.” But there is more and more pressure to “reduce the C footprint” and sequester more C. As discussed at the most recent Louisiana Forage Conference in Alexandria (Dec. 2022), one of the most effective ways to sequester C is by growing more forage and increasing organic matter in the soil.
When we add clover to a bermudagrass or bahiagrass pasture, we extend the forage growing season, we produce more forage dry matter and we make capture more CO2. Plants are about 90% C and O, so 2000 lb of forage dry matter per acre is equal to capturing about 1800 lb per ac of C and O. Since clovers are cool-season plants, they grow in colder periods of the year when summer perennials are dormant, providing both grazing opportunities and carbon sequestration.
Adding a clover to your grazing mixture has many advantages. But which legume to plant? That is the topic for next time.