Soil Management for Pastures and Rangelands
Grazing Management Practices
Within managed ecosystems, such as pastures, soil physical, chemical, and biological properties may be severely compromised. Continuous grazing can affect soil properties and health by reducing soil carbon stocks and other available nutrients, while creating bare patches in vegetation that may enhance erosion and runoff. In contrast, practicing managed grazing within a perennial pasture system has the potential to improve soil properties such as soil carbon stocks, soil structure, as well as nutrient and water retention. There are a number of management practices that can be implemented to control grazing and increase the sustainability of grazing operations.
Paddock Size
As mentioned before, livestock grazing contributes to nutrient cycling and increases soil organic matter. Managed grazing allows for uniformity of paddock defoliation but also encourages uniformity of manure distribution within the paddock. The spatial distribution of manure can be managed in many ways: for instance, by the size and shape of the paddock, the placement of water sources, and the number of animals on the paddock.
Stocking Density
Stocking density (i.e., number of animals per unit area) also plays a large role in managing soils. Stock density is usually expressed in pounds of animals per acre. As the pounds per acre of livestock increases, stock density also increases. Many grazing operations do not adequately consider the impacts of stock density when planning and managing pastures. On any operation, it is critical that the stocking rate match the available forage. As stocking density increases, regardless of grazing system, animals will walk over an area multiple times which can lead to a breakdown in soil structure, especially when soils are wet.
Controlled Access
Livestock are controlled to improve utilization of plants and reduce both overgrazing and spot grazing. By restricting animals’ access to the pasture, only portions of the field are grazed at any given time, allowing all the plants (including weeds) to be grazed more evenly while the remainder of the pastures are allowed to rest and recover. Improved fencing approaches (both for materials and rapid installation) and efficient watering technology is revolutionizing how farmers keep and move livestock.
Utilization Rate
Utilization rate refers to grazing intensity and is a term often used to describe how heavily an area is grazed. For example, if a plant is grazed as close to the ground as possible, the utilization rate would be 100 percent, whereas if the same plant was not grazed, its utilization rate would be 0 percent.
Seasonal Grazing Challenges
Spring grazing creates a new set of challenges. In the spring, plants are just beginning their seasonal growth and are extremely susceptible to overgrazing. Overgrazing plants in the spring can set back growth for the entire growing season. Many grazers make the mistake of grazing plants too hard or too early in the spring and the result is often a significant reduction in overall pasture yields over the course of the year. Waiting to graze a field in the spring allows the plants to develop deeper roots that can better access water and nutrients in the soil profile. This also allows the plants to build more leaf area (think solar panels) to capture more sunlight and increase their rate of growth. If early spring grazing is unpreventable, supplemental hay may need to be fed on the pasture to reduce the risks of overgrazing young plants. If a pasture is grazed early in the spring, make sure that the following year that same pasture is not grazed until later in the season.
Rest and Recovery
Increases in bulk density in intensive grazing systems is reversible given adequate time for recovery. Recovery begins within a few weeks once animals are removed from a paddock but if the compaction is severe, it can take 1 to 4 years of grazing exclusion to recover to levels approaching pre-trampling conditions. Even though complete recovery is a long-term process, significant improvement has been noted to occur within 6 months of grazing exclusion, especially in the top 2 to 4 inches of soil. Rest allows the soil to be free of impact for a period of time and for root growth and other biological activity to aid in remediation
Plant Biodiversity
Within the broad range of plant biodiversity in pastures, plant species diversity may be the most amenable to manipulation or management. Reported benefits of plant diversity in grasslands include increased forage production, greater ecosystem stability in response to disturbance, and reduced invasion by exotic species such as weeds. Some view diversity as a sort of insurance policy where different species contribute in their own time or can take the place of species that fail from stress or mismanagement. Using mixtures of several forages in pastures, in some instances, can improve forage yield and reduce weed invasions.
Improving Drainage
Grazing animals, especially cattle, damage the soil when walking over wet land, leaving deep hoof marks that trap rainwater. In some low-lying areas, a well-designed drainage system may be necessary to carry surface water away and/or to lower the ground water table below the pasture’s root zone (Section 22.3).
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