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Grazing for soil health

Victor Shelton Published on 12 November 2014
Jake Billington moves cattle

I occasionally have some dried mud on my boots. If not cleaned well enough, that mud might end up as dirt on the floor.

Out in the field, whether cropland or pasture, it certainly should not be called dirt, but soil. Depending on the site and how it was formed, the soil will contain different amounts of sand, silt, clay and organic matter. But soil is more than just an inert medium – it is also alive.

There is a lot of talk about soil health these days, so this should not be any surprise to most producers. You know the more fertile the soil, the better the forages you can grow on it, but there is much more to it than just that. We need to maximize the potential of the soil resource.

The soil is not just a growing medium; it is a potential powerhouse of biological activity. By keeping the soil healthy, you then have healthier and increased forage production.

Maintaining adequate fertility and the right pH is a good start. But we must also protect, maintain or ideally build soil organic matter, too.

Soil quality has been talked about by NRCS for a long time. Soil quality is the functional ability of the soil to support optimal biological activity and diversity for plant and animal productivity, to regulate water flow and storage, and to provide an environmental buffer.

Soil health, on the other hand, which some may call the latest buzz words of NRCS, is much more than soil quality. Soil health is the continued capacity of the soil as a vital living system whereby plant and animal growth and environmental quality is sustained. It requires a holistic approach in which plants, animals and human health is promoted.

Soil health is a journey, not a destination. You don’t really know what the true ultimate potential is. There is not a certain point in time that once you reach it, you can say, “I’m here.”

Instead, managing for soil health is constantly changing and constantly needing to be not just maintained but moving forward.

What should you be finding with increased soil health? What is talked about more than anything else is increasing amounts of soil organic matter.

Just a 1 percent increase in soil organic matter is a big deal. It was once thought it took very long periods of time to increase soil organic matter; we know now it can be achieved in a fairly short period of time.

However, it is very important that we don’t do anything that will cause it to decline, only increase.

One percent soil organic matter in the soil equals about 20,000 pounds per acre. Soil organic matter holds about 20 times its weight in water.

Each 1 percent of organic matter contains approximately 10,000 pounds of carbon, 1,000 pounds of nitrogen and 100 pounds of phosphorus and sulfur.

There are values to these nutrients, but what should excite you even more is the soil’s ability to hold approximately an extra 14,400 gallons of water per acre. How valuable is that in a drought?

What breaks down organic matter? Tillage is very hard on soil organic matter because it exposes the carbon to oxygen, which oxidizes it.

On pasture, we normally don’t have this kind of disturbance, but we can have what could be considered vertical erosion. Soil should contain about 50 percent minerals, 25 percent air and 25 percent water.

Overgrazing causes inadequate vegetative canopy and duff, and with the combination of hoof traffic and solar impact, quickly degrades aggregates and organic matter.

Soil density increases, “filling in” valuable air and water pore space (compaction) and reducing the water-holding ability and breaking down valuable organic matter in a now-anaerobic condition, which also increases runoff.

A good healthy soil is granular in nature, and water moves downward through it, creating a good aerobic condition for the surface layers … like a sponge.

The more organic matter present, the higher the infiltration rate and thus less runoff. When it rains, we want as much of the rainwater to be absorbed by the soil as possible.

That does not mean water-logged soils. Soils that are water-logged or oversaturated have drainage issues, limiting layers or compaction.

It is truly amazing to realize that your soil health is improving and where you were once seeing heavy amounts of runoff, you are now capturing and storing more water in your water “bank account.” This is most easily seen in fields that contain water and sediment control basins or dry dams.

Where water once pooled in these structures, even with a small rain, with increased infiltration and more water-holding capacity you find less and less water present in these structures after a rain event. The increased filtration not only helps store water for later use but also reduces flooding.

Roots and the soil biota need air to breathe and thrive. The more biological activity we have in the soil, the more potential for extra biologically produced nitrogen and increased availability of nutrients.

Improving soil health also means improving nutrient cycling and balancing plus diversifying soil biology. It doesn’t matter if we talk about pasture or cropland; the principles are the same.

It might just be easier on pasture. You want to maximize soil cover, certainly minimize any disturbance, provide continuous living plants and roots, and maximize the diversity of plants.

OK, here is a good spot to talk about management. Like I’ve said before, cover is so important. Growing, dormant and decomposing plant material are all cover and play a part.

Besides covering the soil to help maintain moisture reserves, reduce runoff and erosion, and assist with maintaining or building organic matter, live plants are needed for photosynthesis.

We want that “solar panel” working and capturing as much solar energy as possible. Bare ground does not capture and utilize much sunlight. Mature forage does not make a very good solar panel either.

Maintain good “stop grazing” heights. That means remove or move livestock when forages are grazed to about 4 inches (shortest height for most cool-season forages) and 8 inches for most warm-season forages.

This helps maintain the plant’s solar panel and roots. We need growing live roots with the ability to go down deep for moisture as things start turning dry and to also move nutrients deeper in the profile toward the surface.

Typically, the amount of live plant above-ground is somewhat proportional to the amount of live roots. Removing top growth also affects the plant below-ground.

As a rule, “taking half and leaving half” allows leaves to be removed while not slowing down root growth.

Adequate rest is needed for the plant to recover before being grazed again. Protecting that solar panel, maintaining deep live roots and keeping the ground covered are our defenses to potential hot, dry weather and improving soil health on pasture.

These practices also keep the soil cooler. Soil at 70ºF (measured at 2-inch depth) will make available 100 percent of the moisture present for plant growth use.

As soil temperatures rise, less moisture is available for plant use and is lost through evaporation and transpiration. At 95ºF, soil organic matter also starts to break down. Keeping the soil covered and cool is critical to pasture soil health.

Improving soil health with all its attributes is a journey leading to increased production and a contingency plan with resilience. It is exciting to try and visualize where it could take us. Keep on grazing!  FG

Jake Billington moves cattle in southern Idaho to maintain good “stop grazing” heights, which means moving livestock when warm-season forages are grazed to about 8 inches. Photo by Lynn Jaynes.

Victor Shelton
  • Victor Shelton
  • NRCS State Agronomist and Grazing Specialist