Eradicating Pasture Erosion

Keeping a healthy pasture turns out to be a lot like keeping a healthy horse; learn what is normal, learn what can go wrong, then monitor that the former is not becoming the latter

Erosion happens when the horses' grass consumption rate is greater than the grass' growth rate. "It's called getting ahead of the pasture," says Glen Aiken, MS, PhD, a research animal scientist at the USDA Agricultural Research Service's Forage Animal Production Research Unit in Lexington, Ky. Think of him as the grass guy.

When desirable grass species cannot keep up with demand, the plant population in the pasture changes and undesirable (i.e., weed) species grow up. Many weeds produce stems that grow more upright than grasses. This can contribute to erosion, as weeds leave bare patches of ground around their stems and have less of a root network. The more horses graze, the more grass root death you will have. Less root density means less stable soil. This becomes important if the patch of ground is on a slope, and, explains Aiken, not much of a slope is required. "If we didn't have grasslands, we wouldn't have topsoil. It would all be in the rivers," he says.

Therefore, one element to preventing erosion is to maintain a good stand of grass.

Fixing pre-existing erosion will probably entail a visit by a county extension agent or a pasture management consultant. Options would be to reduce the number of horses, lime and fertilize, or, in cases of major deterioration, to start over. A pasture with a high encroachment of weeds might need to have the weeds killed, the ground cultivated, and grass replanted. Aiken explains that a frequent mistake is to put horses back onto replanted pasture too soon. This is one of the considerations when you decide which grass to plant. The grass needs to have time to get firmly established or you waste your effort.

Understocking of animals can also lead to erosion, as horses overgraze on the younger, more tender plants, and the rest of the field grows past the tasty stage. In that case the pasture is said to have gotten ahead of the horses, and mowing would be the answer.

Cutting-edge grass research is exploring the idea of combining forage grasses with grasses that can handle more traffic. Much of the current forage research centers on cattle farms, which demand maximum nutritional value for their grass. Horses, on the other hand, are often supplemented with grain and hay. A horse pasture is a place for exercise and entertainment as much as for nutrition. Therefore, Aiken thinks that horse producers might be interested in seed blends that combine, for example, a forage-type Bermuda grass with a turf-type Bermuda grass.

Although the nutritional value is less, turf grasses have been selectively bred to be low-growing with a dense canopy. Turf that stands up to football games might stand more of a chance against galloping steel-shod hooves.

At Ground Level

In addition to cutting off blades of grass, horse hooves compact the ground, which also leads to erosion. Mark Walker, MS, PhD, a hydrologist at the University of Nevada in Reno, studied the effect of hoof impact on water flow over soil. The result: "When the soil is compacted and vegetation is clipped down to the surface, water flows with more energy than it might if infiltration is happening and vegetation introduces friction."

The water flows with more energy because there is more water on the surface and less to slow it down. When a drop of water hits the ground it either sinks in or rolls away. The difference between saturation or runoff depends on the amount of water and the speed it is moving.

The deeper the water, the more gravity is pushing the water into the ground. Water is also pulled into soil through capillary action in which the surface tension of water pulls it down into small holes in the soil. In Nevada, these holes come from cracks in the soil. In more temperate climates, each blade of grass is a small passageway for water. Compacted ground has fewer of these small passageways, decreasing absorption and increasing runoff. Faster surface flow means more energy to carry away bits of topsoil.

Water in soil can help "fluff up" compacted ground. During a freeze/thaw cycle, water in the soil expands as it freezes, expanding the soil with it.

Erosion carries off upper layers of soil, which are rich in nutrients, fungi, insects, and worms. Stripped soil is less productive. Walker points out that runoff also can contain undesirable elements: "Soil particles can carry pesticides and nutrients, especially phosphorus. Phosphorus can be released from soil particles under some conditions and, if the sediment ends up in a reservoir or lake, it can contribute to aquatic plant and algae growth. Both can change the clarity of a lake."

What Can You Do?

What can you do about erosion? "It depends," says Dennis Thompson, the National Range and Grazing Land Ecologist with the Natural Resources Conservation Service (NRCS), a USDA agency. The NRCS began in the 1930s to fight erosion, first as the Soil Erosion Service, then the Soil Conservation Service, then the NRCS. Thompson agrees with Aiken that the number one cause of erosion is when the vegetation is not healthy enough to prevent it. This loss of cover can come from mismanagement, the number of animals, the wrong plants, or plants in the wrong place.

There are no clear answers to preventing or fixing erosion because each farm situation is different. First thing, Thompson says, is that you need plants adapted to your local area. Ask your extension agent. You also need plants and grass species that are adapted to your particular use. Is this forage in a pasture, or is it ground cover to shore up steep banks?

Independent of the plant cover, how prone to erosion is that piece of ground? We have already mentioned slope. Steeper land is more likely to have faster, more energetic runoff. What is the climate? How much rain, snow, or flooding do you get? This, too, impacts erosion estimates. In addition, some soil types are more prone to erosion.

Other questions to ask include how many animals are on the land? For how long each day? How much will you supplement grazing with hay and grain? In short, what are you asking of your grass? The goal is to match the production capacity of your pasture with your animals' needs.

What is the state of the land? Are you preventing or fixing erosion? Once started, erosion is hard to stop.

Finally, what do you want to put into maintaining your land, and how much time do you have for the task?

One cost-free step is to check your pastures for signs of stress: new plants, weeds, open spots, or horses grazing near manure piles. Thompson recommends that landowners keep their eyes open. "I think the key to whatever they do is continually watch that grass," he says. "They do that, they're going to start to see things that they may not have seen before."

You've heard it before--rotate your pastures. Thompson recommends resting the grass for two to three weeks, even if only occasionally. The exact time depends on your grass and the number of horses grazing it. Although not ideal, an alternative to rotational grazing would be rotational mowing. With fast-growing grasses, you would mow one-sixth of the field every four to five days. Horses will gravitate toward fresh regrowth in the mowed areas, thereby distribute the grazing pressure. Other areas of the country with less hospitable climates for grass will require different schedules.

Walker says another way to practice rotational grazing is to rotate your fence. Instead of building separate areas and moving the horses, build a sturdy perimeter fence, then use light portable fencing (such as electric tape) to direct the horses.

Thompson and Aiken both recommend periodically moving feed and water areas. The cattle industry already has portable water technology. In addition to shifting the horses to different areas, moving the hay will prevent one area of grass from being smothered by a permanent hay cover. Also, split feed and water areas. In the winter when grass is low and feed is next to water, horses have no motivation to move from that spot.

Unavoidable traffic areas--for example, at a gate--might require gravel or terracing to control water runoff. High-traffic areas at big farms might require engineering work: excavation, an underroad fabric, layers of rock, and a cover to walk on. For more details consult the publication Conservation Practice Standard, Heavy Use Area Protection, available from NRCS. (There is more information on the NRCS Web sites, for example, on the NRCS Soils Web site,, the Soil Survey tells me the soil on my farm in Alabama is 75.8% Decatur silt loam.)

To learn the local plants and soil, Thompson has success with pasture walks. Gather a group, a pasture expert, and a willing landowner, then start walking. With this local approach, you see situations that have the same soil, grass, and weather as your farm. You can share information with others who understand the specific problems of spring mud season or summer drought.

How do you eradicate erosion? Know the soil, find the right plants for your purpose, and maintain your pastures with adequate livestock, mowing, and TLC.


About the Author

Katherine Walcott

Katherine Walcott is a freelance writer living in the countryside near Birmingham, Al. She writes for anyone she can talk into paying her and rides whatever disciplines she can talk her horses into doing.

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