But strategies like capturing and storing the carbon emissions from biofuel-burning power plants, or planting new forests to absorb carbon, can create their own problems. If used on a scale large enough to be effective, they would require too much land, water, or energy, or are too expensive. Sequestering carbon in soil, however, is a relatively natural way of removing carbon dioxide from the atmosphere with fewer impacts on land and water, less need for energy, and lower costs.
Better land management and agricultural practices could enhance the ability of soils to store carbon and help combat global warming. If we can figure out how to manage that soil carbon pool size, it could be really effective. Soils in hot or dry areas store less carbon.
How much carbon soils can absorb and how long they can store it varies by location and is effectively determined by how the land is managed. Because almost half the land that can support plant life on Earth has been converted to croplands, pastures and rangelands, soils have actually lost 50 to 70 percent of the carbon they once held.
This has contributed about a quarter of all the manmade global greenhouse gas emissions that are warming the planet. Tilling the soil.
Agricultural practices that disturb the soil—such as tilling, planting mono-crops, removing crop residue, excessive use of fertilizers and pesticides and over-grazing—expose the carbon in the soil to oxygen, allowing it to burn off into the atmosphere. Deforestation, thawing permafrost , and the draining of peatlands also cause soils to release carbon.
Photo: DM. Through photosynthesis, plants absorb carbon dioxide from the atmosphere. They use water and sunlight to turn the carbon into leaves, stems, seeds and roots. As the plants respire, they return some carbon dioxide to the atmosphere and exude some carbon as a sugary substance through their roots. This secretion feeds the microbes bacteria, fungi, protozoa and nematodes that live underground.
When the plants die, soil microbes break down their carbon compounds and use them for metabolism and growth, respiring some back to the atmosphere. Because microbial decomposition releases carbon dioxide, the soil can store more carbon when it is protected from microbial activity. One key way that happens is through the formation of soil aggregates. This occurs when tiny particles of soil clump together, sheltering carbon particles inside them.
Mycorrhizal fungi, which produce sticky compounds that facilitate soil aggregation, are able to transfer 15 percent more carbon into the soil than other microbes. Soils with high clay content are also able to form chemical bonds that protect carbon from microbes. These aggregates give soil its structure, which is essential for healthy plant growth.
Some carbon, made up mainly of plant residue and the carbon exuded by plant roots, remains in soil only for a few days to a few years. Moreover, some scientists believe soils could continue to sequester carbon for 20 to 40 years before they become saturated. Most crops are annuals, so after harvest, fields are often left bare. Leaving crop residue in the ground or planting cover crops that are not to be harvested, like clover and legumes, can compensate for carbon losses from tillage by putting more carbon into the soil. Cover crops in a California orchard. Photo: USDA.
Crop rotation and the use of diverse crops, especially those with deeper roots such as perennials, add more varied biomass to the soil some of which might be more resistant to decomposition and hence more carbon.
When tillage is minimized, soil carbon is not exposed to oxygen and soil aggregates remain intact, sheltering their carbon. Rotational grazing helps keep carbon in the soil by moving herds to new pastures after grazing, allowing old ones to regrow. In addition, carbon in the form of manure gets spread around. Manure and compost increase soil productivity and the formation of stable carbon that can remain in the soil for decades.
Since temperature and precipitation affect the distribution of organic matter and the amount of carbon in soils, how will climate change alter these carbon reservoirs? Earlier studies that heated soils 5 to 20 cm deep found that the soil would release 9 to12 percent more carbon dioxide than normal. Mycorrhizal root tips. This situation has generated interest in developing strategies for reducing GHGs build up in the atmosphere. Out of the approximately 8. The unaccounted difference of 4. This realization has generated interest on the potential of terrestrial sector including soil to sequester carbon in long-lived pools thereby reducing the amount that is present in the atmosphere [ 3 , 4 , 13 , 14 ].
Apart from reducing the concentration of greenhouse gases GHGs in the atmosphere, soil carbon sequestration also complements efforts geared at improving land forest or agricultural land productivity. This is because all strategies that sequester carbon in soil also improve soil quality and land productivity by increasing the organic matter content of the soil.
Carbon sequestration activities offer an opportunity for regaining lost productivity especially under agricultural systems. Apart from climate change mitigation and improving forest land productivity, carbon sequestration in soils of different ecosystems also have several ancillary benefits. Some of these include: improvement in water holding capacity and infiltration, provision of substrate for soil organisms, serving as a source and reservoir of important plant nutrients, improvement of soil structural stability among others [ 13 ].
Based on these reasons, therefore, any policy, strategy or practice that increase soil carbon sequestration also generates these benefits. The obligation on countries, that are parties to the UNFCC, to deposit their independent nationally determined contributions INDCs requires a comprehensive estimation and valuation all carbon sink and sources in the terrestrial and other sectors.
Carbon inventory is a process of estimating changes in the stocks emission and removals of carbon in soil and biomass periodically for various reasons [ 35 ]. Although there are a lot of opportunities in leveraging carbon stock and sequestration potential in the soil of different ecosystems, there are numerous challenges making this difficult in reality.
Some of these challenges include: Measurement and verification : the stock of carbon in soils is difficult, time-consuming and expensive to measure. The annual incremental stock of carbon in soil is very small usually within 0. It is even more difficult to account for little gains or losses in soil carbon at various scales due to methodological difficulties such as monitoring, verification, sampling and depth [ 38 ].
Even if these small changes gains or losses are detected, it is not easy to link such changes to management or land use practice in a given context. The capacity of the soil to sequester and retain carbon is also finite as it reaches a steady state after sometime. Carbon pools : sequestered carbon exists in the soil in different pools with varying degree of residence time in the ecosystem. These pools include:. Passive, recalcitrant or refractory pool: organic carbon held in this pool has a very long residence time ranging from decades to thousands of years.
Active, labile or fast pool: carbon held in this pool stays in the soil for much shorter period due to fast decomposition. The residence time normally ranges from 1 day to a year. Slow, stable or humus pool: carbon held in this pool has long turnover time due to slow rate of decomposition. The residence time typically ranges from 1 year to a decade.
Permanence : another challenge of carbon sequestration in soil is non-permanence of the sequestered carbon as it can be released back to the atmosphere as easily as it is gained as a result of decomposition or mineralization. It is for this reason that sequestered carbon is considered a short-term option for removing carbon from the atmosphere. The rate of carbon loss depends on several climatic, land use and management factors.
Separation : it is very difficult to isolate and differentiate the portion of carbon sequestered in the soil as result of management activities or land use and that which occurred naturally. The principle of separation requires that the carbon sequestered or GHGs emission prevented as a result of management intervention be distinguished from that which would have occurred due to natural causes.
Methods are therefore needed that can differentiate naturally sequestered carbon from that captured due to human management [ 39 ].
Soil carbon sequestration can play a strategic role in controlling the increase of CO2 in the atmosphere and thereby help mitigate climatic change. There are. Semantic Scholar extracted view of "Storing carbon in agricultural soils: a multi- purpose environmental strategy" by Norman J. Rosenberg et al.
There are proven practices and strategies that lead to increase in soil carbon stock in different terrestrial ecosystems. Most of these strategies increases the carbon stock in biomass through photosynthesis and indirectly builds up below ground and soil carbon through increased deposition of organic matter. According to Post and Kwon in , organic carbon level of soil can be improved by increasing the amount of organic matter input, changing the decomposability of organic matter, placing organic matter in deep layer and enhancing better physical protection of the soil aggregates or formation of organo-mineral complexes [ 14 ].
In the forest ecosystem, the following have been widely reported. Increasing the carbon stock of existing forests using several silvilcultural techniques among others [ 40 , 41 , 42 , 43 ]. In the agricultural ecosystem, some strategies that enhance carbon capture and storage in the soil include: Manuring and fertilizing. There has been increasing interest on carbon capture and storage in the soils of different ecosystems as a climate mitigation measure.
However, enhancing the carbon stock of soils also have ancillary benefits such as improving soil health and productivity, water retention, fertility enhancement among others. Although, theoretically this idea sounds appealing, however it is difficult to operationalize it in practice due to a number of challenges. Some of these include difficulties in measurement of soil carbon stock, permanence, carbon pools with different carbon residence times, separation, the tendency of the soil to reach saturation level when the maximum attainable carbon that could be captured is reached.
Advances have been made in tackling most of these challenges, however, deliberate actions to enhance carbon capture and sequestration in the soil ecosystem is yet to get wide acceptance by practitioners and policy makers alike. This chapter is written in an attempt to create more awareness on the potential of soils in capturing and storing atmospheric CO 2 in long lived pools thereby mitigating climate change in the process.
Researchers should also work assiduously in finding solutions to the challenges making widespread adoption of this initiative difficult. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications. Edited by Ramesh K.
By Robert D. Kothera, Benjamin K. Woods, Edward A. Bubert and Norman M. We are IntechOpen, the world's leading publisher of Open Access books. Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Abstract Recently, the contributions of the soil in various ecosystems have become more prominent with the recognition of its role as a carbon sink and the potential of that in reducing the concentration of carbon dioxide CO2 , which is a vital greenhouse gas, from the atmosphere.
Keywords soil carbon sequestration climate change carbon dioxide ecosystem services. Introduction The role of soil the ecosystem is increasingly being recognized with the realization that it has the capacity of reducing the concentration of carbon dioxide CO 2 in the atmosphere through sequestration of organic carbon in the soil and also by releasing this CO 2 back into the atmosphere through mineralization of soil organic matter.
Genesis of the carbon sequestration idea in terrestrial systems The idea that the concentration of CO 2 in the atmosphere can be minimized by sequestering it in terrestrial ecosystems, including the soil was first proposed by Dyson in [ 10 ].
Mechanisms of carbon capture and sequestration Soil carbon is originally derived from the CO 2 assimilated by plants through photosynthesis and converted to simple sugars and eventually returned to the soil as soil organic matter. Carbon sequestration Carbon sequestration is the process of transferring carbon dioxide CO 2 from the atmosphere into stable terrestrial carbon C pools. Carbon stock in forest soils Carbon is stored in forest ecosystems mainly in biomass and soil and to a lesser extent in coarse woody debris [ 25 ]. Carbon stock in agricultural soils According to the IPCC agricultural soils have the potential of sequestering up to 1.
Contribution of Soil to Greenhouse Gas Inventories 5. Several calculators have been developed for such purpose but more precise information is needed to guarantee an accurate accounting of GHGs emissions or SOC stocks Colomb et al. Specific examples of potential applications for the accounting of soil C stocks and fluxes of GHGs are discussed below. The amount of carbon sequestered in the soil reflects the long term balance between carbon uptake and release mechanisms. Beare, M. However, when farming practices are changed to increase the organic carbon content of the soil, the reverse occurs: the soil captures more CO 2 than it emits, which means that CO 2 is removed from the atmosphere and stored in the soil. Change Biol.
The role of soil carbon in different ecosystems The carbon in soil plays significant roles in different ecosystems. Some of these include: 5. Mitigation of climate change The continuous increase in the concentration of carbon dioxide CO 2 and other GHGs in the atmosphere largely due to anthropogenic sources is believed to be responsible for climatic changes and related consequences being experienced across the globe [ 21 , 23 ]. Sustainable land management Apart from reducing the concentration of greenhouse gases GHGs in the atmosphere, soil carbon sequestration also complements efforts geared at improving land forest or agricultural land productivity.
Ancillary benefits Apart from climate change mitigation and improving forest land productivity, carbon sequestration in soils of different ecosystems also have several ancillary benefits. Carbon inventories The obligation on countries, that are parties to the UNFCC, to deposit their independent nationally determined contributions INDCs requires a comprehensive estimation and valuation all carbon sink and sources in the terrestrial and other sectors.
Challenges of carbon sequestration in soils Although there are a lot of opportunities in leveraging carbon stock and sequestration potential in the soil of different ecosystems, there are numerous challenges making this difficult in reality. These pools include: Passive, recalcitrant or refractory pool: organic carbon held in this pool has a very long residence time ranging from decades to thousands of years.
Strategies of increasing carbon stock in soils There are proven practices and strategies that lead to increase in soil carbon stock in different terrestrial ecosystems. Afforestation Reforestation Natural regeneration Enrichment planting Reduced impact logging RIL Increasing the carbon stock of existing forests using several silvilcultural techniques among others [ 40 , 41 , 42 , 43 ].
Conclusion There has been increasing interest on carbon capture and storage in the soils of different ecosystems as a climate mitigation measure. More Print chapter. How to cite and reference Link to this chapter Copy to clipboard. Available from:.