Assessing land condition due to drought is as important, if not more so, than scoring animal body condition. Herd condition will not improve until the land can produce enough forage to allow cattle weight gain. Much vegetation on drought stricken pasture and rangeland has been grazed to the ground leaving a large percentage of bare areas. Drought ravaged grazing land needs three things to rebound– vegetative cover, rest and plant diversity.
Ray Achuleta, Agronomist with the United States Department of Agriculture Natural Resources Conservation Service (USDA-NRCS) says, “A vegetative cover is needed on soil 24 hours a day, 7 days a week to build organic matter, hold water and stop erosion. Continuous live or dead cover helps maintain soil health and protects it from heat and raindrop impact. Soil needs armor.”
“A healthy soil has a functioning ecosystem that contains organic matter, earthworms and micro-organisms (bacteria, fungi and protozoa),” continues Achuleta. “Eighty percent of our plants are mycorrhizal, meaning they have a symbiotic relationship with fungi. Carbohydrates are translocated by plants to their fungal partners, and in return, the plant gains benefits from the fungi’s higher absorptive capacity for water and minerals. Through the absorption process, the fungi coats soil particles with a glomalin protein.”
“Glomalin is an important molecule in soil aggregate stabilization,” says Kris Nichols, United States Department of Agriculture Research Service (USDA-ARS). “Unstable aggregates break apart with rainfall that may cause organic matter and nutrients to be lost to water and wind erosion. High glomalin concentrations are related to the formation and stabilization of aggregates in healthy soils.”
Earthworms normally inhabit soil that contains organic matter. They are major decomposers of dead and decomposing organic matter and derive their nutrition from the associated bacteria and fungi.
Bare soils reach extremely high temperatures that kill earthworms and micro-organisms. The soil ecosystem quits functioning and the ground becomes unproductive.
Charles Kneuper, Rangeland Management Specialist with USDA-NRCS measured soil temperature in North Central Texas during early June, 2011. The ambient air temperature was approximately 105oF and soil temperature at the surface of bare ground was 165oF. At two inches deep in the bare ground, soil temperature was 144oF. In a nearby area covered with little bluestem grass, soil temperature at two inches deep measured 100oF. In 1956, J.J. McEntire, USDA-NRCS found that soil bacteria died when soil temperature reached 140oF. These data show that vegetative cover cools soil and is important for protecting soil micro-organisms.
Plant leaves continuously removed by grazing or other harvesting techniques are required to constantly replace the removed forage in order to survive. Under these demands, plants deplete their carbohydrate storage and are unable to produce additional growth. They eventually die and are replaced with plants less palatable to cattle.
Carbohydrates are produced in a plant from the sun’s energy through a process called photosynthesis. They are manufactured in the leaves and stored in the stem bases (plant crowns), roots and rhizomes. Plants use carbohydrates to grow leaves and tillers. Stored carbohydrates keep plants alive during periods of stress such as drought and winter. For pastures to rebound from drought, they need rest so that the plants can rebuild their carbohydrate reserves and grow more foliage.
Building soil health is like putting weight on a cow. To improve soil, you have to feed its micro-organisms, and to increase a cow’s body condition score, you have to properly feed her rumen bacteria.
One way to improve soil health is to plant a variety of plant types that include warm and cool season grasses and warm and cool season broad-leaf plants. Soil micro-organisms are more active when they have a variety of organic matter on which to feed.
Soil Health Remediation
Kneuper says, “The following systems approach uses five principles for remediating drought ravished soil. All five principles need to be addressed for soil health improvement since they are a system and are not as effective when used alone.
- Armor the soil. Bare areas need to be covered to provide shade, retain water and produce organic matter. Planting annual plants on bare ground areas is one option for providing soil armor.
- Minimize disturbance. Grazing is a disturbance that can be managed in a drought situation. We cannot control the drought, but to minimize disturbance, we can manage grazing. Remove cattle and other livestock from pastures in poor condition so the grass can re-establish itself. Do not restock these pastures until the vegetation has fully recovered.
- Plant multiple species of plants to provide variety for the soil micro-organisms. Seed mixtures should contain warm season and cool season grasses as well as warm season and cool season broadleaf plants (including legumes). The plant diversity will help rebuild soil micro-organism populations.
- Keep living roots in the soil soil during the entire year. Roots create channels for soil water, build organic matter and absorb minerals for plant growth.
- Integrate livestock. From a grazing rotation standpoint, we ideally want to put as many cattle as possible on the smallest amount of land for the shortest period of time. This is referred to as high density grazing. Advantages of this grazing system are a more uniform utilization of all plants, even distribution of fertilizer in the form of urine and feces and good soil tilth resulting from soil surface disturbance by cattle hooves. Good soil tilth provides pore spaces in the soil for movement of water, air and nutrients.
“It is important that your grazing system is one that you can implement,” cautions Kneuper. “Stocking rate is most important and then the grazing scheme. Stock density should be based on how often you are able to rotate the livestock.”
Kneuper is quick to emphasize that improvements in soil health may begin in the first season because annual plant roots increase porosity and foster microbiology. Improving soil health, however, is a long-term commitment that cannot be fully realized in one or two years.