As livestock producers, you know very well how forages will impact the growth or productivity of your animals. However, we very seldom think of how our livestock will impact the growth and productivity of our forages. Understanding the impact that grazing or cutting will have on the pasture is critical to achieving stand longevity, productivity, and quality.
Plants capture their energy from the sun, much like a solar panel. They have specialized cells in the leaves called chlorophyll that are able to convert sunlight into carbohydrates. These carbohydrates do for the plant as they do for us- act as energy that support maintenance, growth of the leaves and roots, and produce seeds. After grazing or cutting, most of the “solar panel” or leaves of the plant have been removed. Without much leaf material, the plant is unable to create energy. Thankfully, plants store carbohydrates in their stems and root systems in case of leaf removal. The stored carbohydrates are metabolized and the energy is now available for creating new leaves. As these new leaves are being produced, sunlight can be captured again and the carbohydrate reserves will slowly be replenished. Assuming adequate nutrients and climate, this cycle will continue and plants will prosper- unless they are unable to replenish their carbohydrate reserves. In these cases, the leaf material is being removed from the plant before it has the opportunity to build up the carbohydrate stores. As a result, the energy is constantly stolen from the plant and it eventually dies. This is why allowing proper rest for your pastures or hay fields is critical for stand longevity.
Exactly how long is enough rest for my pasture? Unfortunately, the answer isn’t as simple as a specific number of days. The length of time required for regrowth is most dependent on the height of the forage after grazing or cutting and the amount of moisture present. The more plant material that is left behind, the faster the forages can grow back. Plants store those carbohydrates in different areas throughout the plant, which varies by species. Understanding how each plant grows will provide insight as to how low a plant can be harvested without causing harm.
For example, fescue stores most of its carbohydrates in the stem base. Grazing this plant below two inches will begin to remove significant amounts of energy stores from the plant. By leaving three or more inches, you leave behind more stored carbohydrates, which results in faster regrowth. In contrast, the growth habit of white clover is low to the ground due to a structure called a stolon, which is a stem that runs along the top of the soil. These stolons act as the primary energy storage organ and explain how white clover can be more persistent in overgrazed areas. Both of these forages can be taken much shorter than native warm-season grasses, like switchgrass or gamma grass, as well as some annual crops, like sorghum-sudan or pearl millet. These grasses grow much taller and have a growth point that is risen high off the ground.
This growth point is a critical area of the plant from which new leaves are formed. If this area is removed from harvest, the plant will no longer be able to grow from that tiller. The growth point in both cool season perennial grasses and clover resides at the soil surface, keeping these plants safe from removal of the growth point by grazing or cutting hay. When grazing pearl millet, sorghum sudan, and related grasses, the growth point can be up to 6 inches off the soil surface, so leaving tall residual behind will ensure future grazings or cuttings. It is important to understand at what height you should cut or stop grazing a forage to ensure you don’t stop growth all together.
I’ve mentioned moisture as a critical component to determining forage rest time. In the southeast, it is common to receive upwards of 50 inches of rainfall per year. This results in increased forage productivity and faster recovery periods as compared to drier areas of the U.S. The ample moisture makes this area more forgiving to overgrazing or overstressing our forage plants. However, the better we are at allowing our forages to rest, the better they can handle and recover from periods of drought. By giving plants time to produce those carbohydrates, they expand their root systems. The more extensive the root system, the more likely they are to find moisture in periods of drought. This fact alone is one of the best reasons to pay attention to your grazing height.
I encourage you to determine when your pastures are ready to graze by evaluating the height of the forage, not by the length of time that it has been given to regrow. This chart below outlines the appropriate heights to begin grazing some common southeastern forages. Consider purchasing a grazing stick. This handy tool acts as a yard stick and has the appropriate grazing start and stopping points for common forages. Understanding how livestock grazing or hay production practices impact your forage plants will result in pastures with greater production during periods of drought, higher quality, and overall stand longevity.