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Managing pasture and range soil health

Ciji Taylor Published on 14 July 2014
Earthworm and other soil-dwelling invertebrates

As world population and demand for food rise, keeping soil healthy and productive is of paramount importance.

That’s why a growing number of American farmers and ranchers adopt soil health management systems to improve the health and function of their soil, which is not only good for the land but the farm or ranch, too.

Soil health is the capacity of soil to function as a vital living ecosystem that sustains plants, animals and humans.

The soil operates as a vital, living ecosystem that is teeming with billions of bacteria, fungi and other microbes in a symbiotic relationship with plant communities and crops that are the foundation for agriculture.

“By the year 2050, an estimated nine billion people will join us at Earth’s dinner table, meaning we’ll have to grow as much food in the next 40 years as we have in the past 500 on even fewer acres of land,” says USDA’s Natural Resources Conservation Service Grazing Lands Specialist Kevin Ogles.

“Improving soil health increases the productivity and function of our soil, which offers increased food security in a growing world.”

Soil properties like depth and texture are not easily changed. But dynamic soil properties such as organic matter, structure and water-holding capacity can be changed based on how the site is managed.

Collectively, these soil properties determine how well the soil functions in supporting plants and animals.

NRCS offers conservation practices that help farmers and ranchers improve these soil properties, such as:

  • Improving soil health
  • Increasing organic matter
  • Reducing soil compaction
  • Improving storage and cycling of nutrients
  • Increasing water infiltration
  • Increasing water available to plants

Have you considered the soil health for range and pasture on your farm or ranch? This article covers the science of healthy soils and how they can benefit agricultural operations.

Well managed forage

Building blocks of the land: soil aggregates
Soil aggregates are the basis for movement of air, water and plant nutrients through the soil profile.

They are groupings of soil particles bound together by glomalin, or “soil glue,” produced when soil biota break down dead, underground plant materials and old roots.

Small soil aggregates are bound together into larger aggregates, the structural arrangement of which allows water and air to move into the soil profile.

Optimizing live vegetation and litter or plant residue is typically the key to maintaining healthy soil aggregates and aggregate formation.

Conversely, high levels of disturbance tend to degrade the soil structure, which blocks the movement of needed moisture and air and diminishes root penetration.

Increasing organic matter
Soil organic matter is a carbon-rich material that includes plant, animal and microbial residue in various stages of decomposition.

Live soil organisms and plant roots are part of the carbon pool in soil but are not considered soil organic matter until they die and begin to decay.

Roots are the primary source of organic matter. Dead roots and gelatinous materials exuded by plant roots as they grow through the soil are decomposed by soil organisms and converted into organic matter.

Every year, a significant percentage of total root biomass dies and becomes available for incorporation into the soil as organic matter.

One percent of organic matter in the top 6 inches of soil can hold as much as 25,000 gallons of water per acre. Increasing organic matter increases the holding capacity for water, making your land more resilient to extreme weather including periods of drought.

A robust root system is developed when a productive plant community on the surface of the soil assimilates nutrients and processes energy from the sun through photosynthesis.

The roots of forbs and shrubs generally contribute less organic matter to the surface layer of the soil than the roots of grasses, so changes in the composition of plant species have an effect on the organic matter in the soil.

Maintaining a productive plant community on the surface of the soil through judicious grazing management is a major key to maintaining or building soil organic matter.

Reducing erosion
Wind and water erosion take their toll on the long-term soil health in rangeland and pastureland. Topsoil has the greatest amount of organic matter, biological activity and nutrients in the soil profile and is the most susceptible to the effects of weather.

The loss of topsoil diminishes the productive nature of a landscape by breaking down the soil structure, exposing organic matter to decomposition and loss. Plant communities then often shift to less desirable plants, such as from grass to shrub species.

Sediment removed by erosion can also bury plants and roads, accumulate in streams, rivers and reservoirs and degrade water quality.

Some management strategies to minimize wind and water erosion may include:

1. Maintaining/increasing the cover of plants or litter on the soil through the application of good rangeland and pastureland management practices

2. Reducing soil surface disturbances

3. Minimizing grazing and traffic when the soil is wet and thus preventing reduced infiltration caused by compaction

4. Building water bars that direct flow from roads, trails or vehicle tracks across the slope or into existing drainage ways

Reducing compaction
Soil compaction occurs when moist or wet soil aggregates are pressed together and the pore space between them is reduced.

Wet soils do not have the same weight-holding capacity as a soil with normal moisture content or dry soil.

Compaction changes soil structure, reducing the size and continuity of pores, and increases soil density. Compaction usually does not happen all at once but over time.

Pressure exerted on the soil surface by animals, vehicles and people can cause soil compaction.

Compaction limits water infiltration at the surface causing increased run-off and, in some areas, increased erosion.

When the amount of water that enters the soil is reduced, less water is available for plant growth and less moves deeper in the soil profile for later use. This is especially detrimental in years with low precipitation.

Pastures grown on compacted soils with fewer pore spaces will start growth later in the spring and stop growth earlier in both the hot summer months and cool autumn months.

With limited oxygen, plants not adapted to anaerobic conditions will either not persist or will not produce very well.

Roots help to break up compacted layers by forcing their way between soil particles and are the best route to recovery.

Plants with large taproots are more effective at penetrating and loosening deep compacted layers, while fibrous root systems can break up compacted layers near the surface and eventually work their way down deeper.

Large soil organisms, such as earthworms and anthropods, also move soil particles as they burrow through the soil.

Good strategies for addressing soil compaction include:

1. Minimizing heavy use of pastures when soils are wet

2. Moving hay bales in place during dry or frozen conditions

3. Improving or maintaining plant cover and plant production by incorporating longer rest periods that allow for deeper root growth and penetration, and over time, increased organic matter

4. Leaving more stubble height (grass that remains when moving to the next pasture) in your grazing rotation.

You should generally leave 4 inches for most cool-season forages and 8 inches for warm-season forages, but this will vary some by region and forage species.

soil structure is developed and maintained through grazing

Holding water on the land
Infiltration rate is the rate at which soil is able to absorb rainfall or irrigation. Higher infiltration rates allow precipitation to enter the soil profile rapidly, thereby reducing run-off and increasing the opportunity for plants to capitalize on that precipitation.

Infiltration is affected by soil compaction, soil texture, soil structure, soil crusts and above-ground biomass.

Greater productivity can be achieved on pasturelands by managing plant cover and biomass through maintaining optimum plant stubble heights.

By keeping run-off and soil evaporation to a minimum, more water is available for plant growth. The benefits of maintaining proper stubble height of your forage species are rewarded by more available water for plant growth.

“When more available water is stored in the soil profile, grasses and legumes will grow longer during dry weather, more forage will be produced, and the moisture balance is maintained so soil micro-organisms can continue to decompose litter and cycle nutrients,” Ogles says.

The right nutrients
Plant nutrients are used by plants for growth. Uniform nutrient distribution, efficient nutrient cycling and increased soil organic matter can contribute to a reduced need for supplemental fertilizer when soil health on range and pasture is optimized.

Most manure is deposited close to water, shade and feed areas. Strategically locating these areas or managing access to these areas can positively affect manure distribution. Rotational grazing also distributes animal waste on the landscape for optimal nutrient cycling.

Plant diversity
A more diverse plant community can often provide benefits to the landscape and help in maintaining soil health on range and pasture.

Different species of plants in grasslands have different growth forms, both above-ground and below-ground.

Forbs, grasses or shrubs can be perennial, annual, bunchgrass, sod-former, rhizomatous, cool-season or warm-season. These different growth forms often complement each other, allowing for the diverse plant community to more effectively occupy the site.

A diverse plant community may help break up disease cycles and guard against weed invasion. In addition, livestock can eat more forage when complementary plants are available.

When poisonous plants are present, other forage is available, so there is a higher potential for the poisonous plants to be avoided.

“One of the goals of conservation programs offered by the NRCS is to improve the landowner’s soil health,” says NRCS Rangeland Management Specialist Gene Fults.

“Healthy soil is more resilient to erosion and better able to store water through extended drought periods.

“By restoring the health and function of our soil, we can transform production agriculture and make our farms more productive, profitable, resilient and better prepared to meet the challenges of the 21st century,” Fults adds.  FG

Ciji Taylor is a public affairs specialist with the USDA’s Natural Resources Conservation Service.

To get started with NRCS, visit your local USDA Service Center.

PHOTO 1: Earthworms and other soil-dwelling invertebrates contribute to soil porosity and soil structure development and maintenance.

PHOTO 2: Well-managed forages with proper stocking and rotational grazing exhibit more robust root systems that help sustain pastures through drought.
PHOTO 3: Soil structure is developed and maintained through grazing management that incorporates rest periods during the growing season for plant recovery. Photos courtesy of Ciji Taylor.