Pasture Management and Carbon Sequestration: Healthy, Diverse Pastures Are Natural ‘Carbon Sinks’

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Photo by Fotolia/Egonzitter
Does raising cattle necessarily have a big carbon footprint? It depends on how you raise them. Rotational grazing on diverse native grasslands allows the soil to store more carbon.

According to a 2014 report by leading climate scientists, convened by the U.S. National Academy of Sciences and the U.K.’s Royal Society, the atmospheric concentration of carbon dioxide has increased by 40 percent since pre-industrial times. More than half of this increase has occurred since 1970, and of all greenhouse gases in the atmosphere, carbon dioxide plays the most significant role in warming the Earth. To curb the climate crisis, some policymakers and concerned citizens have recommended solutions such as renewable energy development, greater resource efficiency and cleaner cars. Land management deserves a spot on that list. How homesteaders and ranchers manage livestock, and how they manage the pastures those livestock graze on, plays a significant role in atmospheric carbon pollution.

Mainstream pasture-management practices seriously degrade pastureland worldwide. Among the damaging processes are plowing grasslands on highly erodible soils and slopes to plant annual crops, destroying diverse mixtures of native perennial grassland species to plant monocultures of domesticated grasses, overgrazing pastures, and failing to properly rotate grazing livestock. All of these practices reduce the carbon content of soils, thus diminishing soil productivity and exacerbating climate change.

Soil carbon is a central product of photosynthesis and an essential component of healthy soil. Pastures and soils are thus crucial “carbon sinks.” The science works like this: Plants extract carbon in its gaseous form (carbon dioxide) from the atmosphere, and combine the carbon with hydrogen and oxygen to form carbohydrates, which the plants then transport through roots and out to the soil, where fungi feed on the carbohydrates and deliver mineral nutrients back to the plants. This invisible partnership between plants and fungi is the foundation of the terrestrial carbon cycle, as plants incorporate carbon from atmospheric carbon dioxide into carbohydrate biomass, both above and below the Earth’s surface. (Plant biomass averages an impressive 47 percent carbon by dry weight.)

Much of the carbon in stems, leaves and roots re-enters the atmosphere when plants decay, but a portion of it is stored in the soil. Soil carbon will be more secure and long-lasting the deeper carbon is buried, the less the soil is disturbed, and the more the soil is protected from sun, wind and water by perennial vegetative cover. Such protections prevent the carbon from releasing into the atmosphere. That’s also good for the land: Adequate soil carbon is essential for water and nutrient retention. Soils with high carbon content thus resist drought better and are more productive than soils low in carbon.

How does all this translate into smart livestock grazing? Management practices proved to sequester carbon in pastures are easy to implement, and have multiple ecological and economic benefits. Planting diverse mixtures of native or well-adapted perennial grasses and legumes eliminates the need for synthetic fertilizers and increases photosynthetic production compared with planting monocultures of domesticated grasses. However, planting some cool-season domesticated grasses, such as brome and fescue, in pastures can substantially extend the grazing season. Overall, think diversity.

Even in diversely planted pasturelands, though, grazing practices make a big difference. Overgrazing reduces carbon sequestration and productivity, but ranchers can avoid it with a rotational grazing system that incorporates multiple paddocks. Stocking density and rotation time depend on the season, the weather and the health of the soil. A rough guideline is to move animals to a new paddock after they’ve consumed about half of the biomass, and then rest each paddock until new growth is evident. Following these guidelines to foster healthy pastures will store more carbon in the soil, thereby helping to ease global warming.

For more on smart land management, see White’s book Biosequestration and Ecological Diversity: Mitigating and Adapting to Climate Change and Environmental Degradation, available from CRC Press. To read more about the negative effects of industrial agriculture, see Biodiversity Loss and Diseases of Civilization: Hidden Downsides of the Green Revolution. — MOTHER EARTH NEWS