2. Grazing Land

Grazing lands cover almost one-third of the contiguous United States.¹⁵⁴ More than 80% of this land is rangeland, uncultivated land with minimal inputs, while the remainder is cultivated and more intensively managed grazing land, or pasture.¹⁵⁵ Pasture has greater potential for carbon sequestration as a result of its higher biomass unit production, but it requires irrigation or high precipitation levels, making it impractical in much of the arid West.¹⁵⁶

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(Degraded pasture has higher potential for new sequestration since it can be improved more.) Regardless of whether ranchers use pasture or rangeland, well-managed silvopasture systems—those that integrate the production of woody perennials and livestock on the same land—offer substantially more climate benefits than conventional grazing systems.

Expand silvopasture. Silvopasture (often included within the broader term “agroforestry”) is the practice of planting woody perennials on grazing lands. As with agroforestry on cropland, silvopasture offers significant greenhouse gas mitigation potential. Adding trees to grazing lands provides a substantial new source of carbon storage, while also increasing livestock productivity (due to reduced heat-stress loss) and introducing new revenue streams for farmers whose trees produce food or forestry products.

Co-benefits of silvopasture systems include improved water quality, reduced erosion, and additional habitat for wildlife.¹⁶⁰

Limit livestock production to grazing and byproducts. As discussed above, approximately half of all harvested cropland in the United States is devoted to feed crop production.¹⁶¹ Devoting such a high share of cropland to feed production substantially increases greenhouse gas emissions relative to other

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agricultural practices since animal products have a poor feed-to-food conversion rate.¹⁶² A hundred calories of feed, for example, only produces three calories of edible beef.¹⁶³ Eggs and dairy products have the highest conversion rate at 17%, meaning that 100 calories of feed results in 17 calories of eggs or dairy products.

Animal products are not inherently inefficient, however. Animals can be fed with resources that do not contribute to human food consumption, namely grassland unsuited for crop cultivation and byproducts from crop production and food processing.¹⁶⁴ As a result, researchers have proposed limiting livestock production to so-called “ecological leftovers,” or “low-opportunity-cost feed,” in order to render animal products more sustainable.¹⁶⁵ This would likely decrease the amount of animal products available—one study found that such limitations would reduce the amount of animal protein available per capita in the European Union by 40%¹⁶⁶—but it would provide a number of climate benefits.

When produced using ecological leftovers, livestock production can sustain biodiversity,¹⁶⁸ promote the use of perennials,¹⁶⁹ and recycle plant nutrients.¹⁷⁰

Improve grazing management. Grazing practices not only affect methane emissions from the grazing animals themselves but also soil emissions of greenhouse gases. The impacts of grazing on soil carbon storage depend on interactions between precipitation, soil texture, and grassland plant community composition, among other factors,¹⁷¹ but grazing itself generally

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decreases grassland soil, root, and microbial carbon pools.¹⁷² Heavy rates of grazing can even reduce soil greenhouse gas emissions compared to grasslands without grazing.¹⁷³ Due to these interactions, managing rotation durations, stocking rates, and grazing pattern complexity can influence carbon sequestration on grazing lands.

Several factors, including climate, precipitation, topography, local plant communities, soil type, and ranch size, influence the types of practices appropriate for any given location and the magnitude of their impacts on carbon and nitrogen cycling. Management systems that rotate livestock through a series of pastures, if implemented well, may improve grassland productivity, increase soil organic carbon, and reduce greenhouse gas emissions.¹⁷⁴ At the same time, continuous systems, which allow unrestricted grazing, are more likely to lead to soil carbon losses.¹⁷⁵

The USDA Natural Resources Conservation Service (NRCS) includes rotational systems that rotate livestock in order to foster optimal plant and animal health as a component of “prescribed grazing.” There are different types of prescribed grazing systems, such as management-intensive grazing, adaptive multi-paddock grazing, and less intensive forms of rotational and planned grazing.

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The ability of individual systems to sequester carbon has been vigorously debated,¹⁷⁷ varies by region and land use history,¹⁷⁸ and hits an upper limit when soils become saturated.¹⁷⁹ Environmental factors beyond the control of ranchers, such as drought conditions, can also overshadow and overwhelm the impact of even the most effective management practices, particularly in arid rangelands.¹⁸⁰ The net impact of grazing practices on the climate also depends on the balance of specific greenhouse gas emissions and sequestration rates, which may not shift in a consistent direction in response to changes in management. For example, while adaptive multi-paddock grazing reduces soil emissions of nitrous oxide and methane, it may also result in higher CO₂ emissions from soil respiration.¹⁸¹

Advocates of adaptive multi-paddock grazing and other forms of intensive rotational grazing note that current conventional extensive operations can transition to managed grazing in a few years, depending on the region’s climate and that various cost savings, such as reduced forage costs, can occur even before all the carbon benefits start to accrue, thus facilitating the transition.¹⁸² Using a meta-analysis including hundreds of observations, a group of researchers in 2017 found that improved grazing practices (including lower stocking rates, removal of grazing livestock, several types of rotational or short-duration grazing, and seasonal grazing) generally (but not always) increased annual carbon sequestration rates on average by 0.28 metric ton carbon per hectare per year, a significant amount especially if applicable to all or most U.S.

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used, further examples and additional research will likely lead to improved performance and a better understanding of the impact and the regions and land types on which it may be most effective.¹⁸⁵

Rotational grazing co-benefits include increased species diversity, decreased erosion, improved soil quality, better quantity and quality of wildlife habitat, improved water quality, and improved riparian ecosystem health and watershed quality.¹⁸⁶

Optimize feed, breed, and herd health. Grazing practices have been the subject of significant attention and debate; however, ranchers can also take important steps to reduce net emissions through improved feed, breed, and animal health management. By carefully managing their herds’ feed and forage options, operators may be able to decrease enteric emissions.¹⁸⁷ Operators can also reduce emissions by maintaining herd health and choosing or developing breeds best adapted to the local environment.¹⁸⁸ The capacity of different breeds to thrive in local conditions, such as weather and native plant communities, affects how quickly they mature. Breeds optimized for local conditions will therefore reach slaughter weight more quickly, reducing their emissions.

Add soil amendments. New research has demonstrated that organic soil amendments like compost may be able to boost carbon sequestration on grazing land. Over the course of three years, researchers found that a single application of composted organic matter to rangeland increased net carbon

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storage by 25%-70%,¹⁸⁹ while also increasing the production of grass for feed and thereby making rangelands more productive.¹⁹⁰ Some scientists have expressed concern that applying compost on natural grasslands could negatively alter soil chemistry and water quality, favor invasive plants species, and decrease native plant diversity.¹⁹¹ A 2019 meta-analysis of 92 studies found that “organic amendments, on average, provide some environmental benefits (increased soil carbon, soil water holding capacity, aboveground net primary productivity, and plant tissue nitrogen; decreased runoff quantity), as well as some environmental harms (increased concentrations of soil lead, runoff nitrate, and runoff phosphorus; increased soil CO₂ emissions).”¹⁹² Further study and field trials will need to confirm these results and measure results in different ecosystems.¹⁹³