Carbon Management and Sequestration Program
Ohio Agric. Research & Development Center
The Ohio State University
Columbus, OH 43210
SOIL CARBON SEQUESTRATION TO REDUCE NET GASEOUS EMISSIONS
Committee on Environment and Public Works
628 Dirksen Senate Office Building
2 May 2001
SOIL CARBON SEQUESTRATION TO REDUCE NET GASEOUS EMISSIONS
Mr. Chairman, members of the Committee on Environment and Public Works. I am Rattan Lal, Professor of Soil Science and Director of the Carbon Management and Sequestration Program at The Ohio State University. I am especially thankful to Senator Voinovich for the opportunity to offer testimony on “Soil Carbon Sequestration to Reduce Net Gaseous Emissions.”
Let me begin by expressing my appreciation of strong cooperation with several institutions and organizations across the country. During the past decade, the program at The Ohio State University (OSU) has been supported by USDA-Natural Resource Conservation Service (NRCS). I cannot thank NRCS enough for its past, present and future support. We have also worked with scientists from USDA-Agricultural Research Service (ARS). The multi-institutional team comprised of OSU/NRCS/ARS has published 12 books, which constitute a major literature on this topic. In addition, OSU also has on-going programs with the Pacific Northwest National Laboratory and the Oak Ridge National Laboratory. Being a founding member of the “Consortium for Agricultural Soils Mitigation of Greenhouse Gases (CASMGS),” the OSU team is collaborating with faculty from ten universities in developing a long-term program on soil carbon sequestration. Following up on the research done for estimating the potential of U.S. cropland and grazing lands to sequester carbon, OSU/NRCS group is now working with USDA-Forest Service (FS) to estimate the potential of U.S. forest soils to sequester carbon. We are presently formulating a program with the Los Alamos National Laboratory, in cooperation with the Ohio Coal Development Office and American Electric Power, to develop a long-term program on soil C sequestration, soil quality and net primary productivity of different ecosystems, with immediate focus on reclamation of mineland sites in Ohio, west Texas and New Mexico. We are also working with USDA-Economic Research Service (ERS) on the topic of soil degradation and its effects on productivity and the C dynamics. We are working with these partners because we share the same values and goals of “sustainable management of soil and water resources, reducing net emissions, and creating a clean environment.”
The basis of our shared commitment is the mutual concern about the quality of the nation’s soil and water resources and the environment. We realize how important and critical the quality of soil resources is for maintaining high economic agricultural production while moderating the quality of air and water. Advances in soil science, especially those in relation to efficient use of water and nutrients by input-responsive and high yielding varieties, broke the yield barriers, ushered in the Green Revolution, and brought about a quantum jump in agricultural production in the post-World War II era. Gains in agricultural production globally during the second half of the 20th century saved millions from starvation, and once again proved the neo-Malthusian views wrong. Now we want to use the knowledge of soil science in addressing another important and global issue of the modern era – reducing net emissions of greenhouse gases into the atmosphere.
The atmosphere is a classic example of a common pool resource that is prone to exploitation. With industrialization and expansion of agriculture, through deforestation and plowing, comes soil degradation and emission of gases into the atmosphere. Indeed, the atmospheric concentration of three important greenhouse gases (carbon dioxide, methane and nitrous oxide) has been increasing due to anthropogenic perturbations of the global carbon and nitrogen cycles. For example, the pre-industrial concentration of carbon dioxide at 280 parts per million (0.028% or 600 billion tons or Gt) increased to almost 365 ppm (0.037% or 770 Gt) in 1998 and is increasing at the rate of 0.5%/yr or 3.8 Pg/yr. The historic gaseous increase between 1850 and 1998 has occurred due to two activities: (1) fossil fuel burning and cement production which has contributed 270 (+30) Gt of carbon as CO2, and (2) deforestation and soil cultivation which has emitted 136 (+55) Gt. Of this, the contribution from world soils may have been 78 (+17) Gt of which 26 (+9) Gt may be due to erosion and related soil-degradative processes. In comparison with the global emissions, cropland soils of the United States have lost 3 to 5 Gt of carbon since conversion from natural to agricultural ecosystems.
Greenhouse gases are released into the atmosphere when trees are cut down and burnt, soils plowed, and wetlands are drained and cultivated. In addition, excessive soil cultivation and inappropriate or inefficient use of nitrogenous fertilizers can result in emission of greenhouse gases from soil to the atmosphere. Finally, accelerated soil erosion can lead to a drastic reduction in soil organic carbon (SOC) content. Although the fate of the carbon that is transported by wind and water is not well understood, it is believed that a considerable portion of the eroded carbon may be mineralized and emitted into the atmosphere. It is estimated that soil erosion annually emits 1.1 Gt of C globally and 0.15 Gt from soils of the United States. Although agricultural processes are presently not the main source of gaseous emissions, they have clearly been a significant source. Yet, the emissions of C from soils are reversible through conversion to a restorative land use and adoption of recommended agricultural practices. These estimates of the amount of lost C, crude as these may be, provide a reference point about the sink capacity through land use conversion and adoption of recommended practices.
Soil organic matter (SOM), of which 58% is carbon, is one of our most important national resources. It consists of a mixture of plant and animal residues at various stages of decomposition and by-products of microbial activity. The SOM is a minor component of the soil (1-3%), but plays a very important role in biological productivity and ecosystem functions. Enhancing SOM content is important to improving soil quality, reducing risks of pollution and contamination of natural waters, and decreasing net gaseous emissions to the atmosphere. The SOM pool can be enhanced through: (1) restoration of degraded soils and ecosystems, and (2) intensification of agriculture on prime soils.
Enhancing the SOM pool is an important aspect of restoration of soils degraded by severe erosion, salinization, compaction, and mineland disturbance. Degraded soils have been stripped of a large fraction of their original SOM pool. There are 305 million hectares (Mha) of moderately and severely degraded soils worldwide. U.S. cropland prone to moderate and severe erosion is estimated at 20.4 Mha by wind erosion and 24.3 Mha by water erosion. An additional 20 Mha are prone to salinization, and 0.6 Mha of land strip-mined for coal is in need of restoration.
Land conversion and restoration transforms degraded lands into ecologically compatible land use systems. The Conservation Reserve Program (CRP) is designed to convert highly erodible land from active crop production to permanent vegetative cover for a 10-year period. In addition to erosion control, land under CRP can sequester carbon in soil at the rate of 0.5 to 1.0 t/ha/year (450 to 900 lbs C/acre/yr). Erosion control also involves establishing conservation buffers and filter strips. These vegetated strips, ranging from 5 to 50 m wide (16.5 to 165 ft. wide) are installed along streams as riparian buffers and on agricultural lands to minimize soil erosion and risks of transport of non-point source pollutants into streams. The rate of C accumulation in soil under conservation buffers is similar to that of the land under CRP. The USDA has a voluntary program to develop 3.2 million km (2 million miles) of conservation buffers.
Wetlands are also an important component of the overall environment. Approximately 15% of the world’s wetlands occur in the United States (40 Mha or 100 million acres) of which 2 Mha (5 million acres) are in need of restoration. Natural wetlands have a potential to accumulate carbon (net of methane) at the rate of 0.2 to 0.3 t/ha/yr (180 to 270 lbs/acre/yr).
Surface mining of coal affected 30,375 ha (75,025 acres) of land in the U.S. during 1998. Restoring minelands, through leveling and using amendments for establishment of pastures and trees, has a potential to sequester 0.5 to 1 t C/ha/yr (450 to 900 lbs C/acre/yr) for 50 years. Similar potential exists in restoring salt-affected soils.
The overall potential of restoration of degraded soils in the United States is 17 to 39 million metric tons or Tg per year for the next 50 years.
Intensification of agriculture involves cultivating the best soils using the best management practices to produce the optimum sustainable yield. Some recommended agricultural practices, along with the potential of SOC sequestration are listed in Table 1. Conversion from plowing to no till or any other form of a permanent conservation till has a large potential to sequester carbon and improve soil quality. There is a strong need to encourage the farming community to adopt conservation tillage systems.
Adoption of recommended practices on 155 Mha (380 million acres) of U.S. cropland has a potential to sequester 58 to 170 Tg C/yr.
Grazing lands, rangeland and pastures together, occupy 212 Mha (524 million acres) of privately owned land and 124 Mha (300 million acres) of publicly owned land.
Total soil C sequestration potential of U.S. grazing land is 22 to 98 Tg C/yr.
The potential of U.S. forest soils to sequester C is 48 to 86 Tg C/yr (Birdsey, 2001).
Thus, the total potential of U.S. agricultural and forest soils (Table 2) is 145 to 393 Tg C/yr or an average of 270 Tg C/yr.
Total U.S. emissions were 1840 Tg CE/yr in 1999 (USEPA, 2000), and are increasing at 2%/yr. Thus, the emissions in 2001 are about 1914 Tg C/yr, of which the contribution of all agricultural practices is 42.9 MMTCE/yr. Therefore the potential carbon sequestration in U.S. soils represents 14% of total U.S. emissions, and 6.3 times the emissions from agricultural activities. Thus, soil C sequestration alone can reduce the net emissions. The U.S. commitment under the Kyoto Protocol is reducing emissions by about 660 MMTCE. Thus, soil C sequestration can account for 40% of the commitment.
The current net C sinks are estimated at 270 Tg/yr, which comprise only 21 Tg/yr of soil C sequestration (USEPA, 2000). If the full potential of soil C sequestration is realized, the total sink capacity can be 519 Tg C/yr (Table 3), which is 78% of the commitment under the Kyoto Protocol. These statistics indicate the need for a serious consideration of determining what fraction of the total potential is realizable, at what cost and by what policy instruments.
There is a widespread perception that agricultural practices cause environmental problems, especially those related to water contamination and the greenhouse effect. Our research has shown that scientific agriculture and conversion of degraded soils to a restorative land use can also be a solution to environmental issues in general and to reducing the net gaseous emissions in particular. Thus, soil carbon sequestration has a potential to reduce the net U.S. emissions by 270 Tg C/yr. This potential is realizable through promotion of CRP, WRP, erosion control and restoration of degraded soils, conservation tillage, growing cover crops, improving judicious fertilizer use and precision farming.
Actions that improve soil and water quality, enhance agronomic productivity and reduce net emissions of greenhouse gases are truly a win-win situation. It is true that soil C sequestration is a short-term solution to the problem of gaseous emissions. In the long term, reducing emissions from the burning of fossil fuels by developing alternative energy sources is the only solution. For the next 50 years, however, soil C sequestration is a very cost-effective option, a “bridge to the future” that buys us time in which to develop those alternative energy options.
1. Birdsey, R. 2001. Potential carbon storage in forest soils of the U.S. Unpublished, USDA-FS.
2. Lal, R., J. Kimble, E. Levine and B.A. Stewart (eds). 1995. Soils and Global Change. Advances in Soil Science, Lewis Publishers, Chelsea, MI, 440 pp.
3. Lal, R., J. Kimble, E. Levine and B.A. Stewart (eds). 1995. Soil Management and Greenhouse Effect. Advances in Soil Science, Lewis Publishers, Chelsea, MI, 385 pp.
4. Lal, R., J.M. Kimble, R.F. Follett and B.A. Stewart (eds). 1998. Soil Processes and the Carbon Cycle. CRC. Boca Raton, FL, 609 pp.
5. Lal, R., J.M. Kimble, R.F. Follett and B.A. Stewart (eds). 1998. Management of Carbon Sequestration in Soils. CRC, Boca Raton, FL, 457 pp.
6. Lal, R., J.M. Kimble, R.F. Follett and C.V. Cole. 1998. The Potential of U.S. Cropland to Sequester C and Mitigate the Greenhouse Effect. Ann Arbor Press, Chelsea, MI, 128 pp.
7. Lal, R., J.M. Kimble and B.A. Stewart (eds). 2000. Global Climate Change and Pedogenic Carbonates. Lewis/CRC Publishers, Boca Raton, FL, 378 pp.
8. Lal, R., J.M. Kimble and B.A. Stewart. 2000. Global Climate Change and Tropical Ecosystems. Lewis/CRC Publishers, Boca Raton, FL, 438 pp.
9. Lal, R., J.M. Kimble and B.A. Stewart 2000. Global Climate Change and Cold Regions Ecosystems. CRC/Lewis Publishers, Boca Raton, FL.
10. Lal, R., J.M. Kimble and R.F. Follett (eds). 2001. Assessment Methods for Soil Carbon. CRC/Lewis Publishers, Boca Raton, FL, 676 pp.
11. Follett, R.F., J.M. Kimble and R. Lal (eds). 2000. The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect. CRC/Lewis Publishers, Boca Raton, FL, 442 pp.
12. Lal, R. and J.M. Kimble. 1997. Conservation tillage for carbon sequestration. Nutrient Cycling in Agroecosystems, 49, 243-253.
13. Lal, R., R.F. Follett, J.M. Kimble and C.V. Cole. 1999. Managing U.S. cropland to sequester carbon in soil. J. Soil Water Conserv. 54: 374-381.
14. Lal, R. (ed) 2001. Soil Carbon Sequestration and the Greenhouse Effect. Special Publication, Soil Science Society of America, Madison, WI.
15. Lal, R. 1999. Soil management and restoration for C sequestration to mitigate the greenhouse effect. Prog. Env. Sci. 1: 307-326.
16. Lal, R. and J.P. Bruce. 1999. The potential of world cropland to sequester carbon and mitigate the greenhouse effect. Env. Sci. & Policy 2: 177-185.
17. Lal, R. 2000. Carbon sequestration in drylands. Annals Arid Zone 38: 1-11.
18. Izaurralde, R.C., N.J. Rosenberg and R. Lal. 2001. Mitigation of climate change by soil carbon sequestration. Adv. Agron. 70: 1-75.
19. Lal, R. 2001. World cropland soils as a source or sink for atmospheric carbon. Adv. Agron. 71: 145-191.
20. Lal, R. 2000. We can control greenhouse gases and feed the world…with proper soil management. J. Soil Water Conserv. 55: 429-432.
21. Lal, R. 2001. Potential of desertification control to sequester carbon and mitigate the greenhouse effect. Climate Change.
22. USEPA 2000. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1999 (draft). EPA 23RR-00-001.
Table 1. Recommended practices for soil C sequestration.
Potential rate of soil carbon sequestration (t/ha/yr)
Conservation tillage & mulch farming
Compost and manuring
Elimination of summer fallow
Growing winter cover crops
Integrated nutrient management/precision farming
Improved varieties and cropping systems
Water conservation and water table management
Improved pasture management
Fertilizer use in forest soils
Restoration of eroded mineland and otherwise degraded soils
Source: Lal et al. (1998); Follett et al. (2000); Birdsey (2000)
Table 2. Total potential of U.S. agricultural soils for C sequestration.
Potential of soil C sequestration (MMT C/yr)
Land conversion and restoration
Intensification of cropland
Improved management of grazing land
Improved management of forest soils
145-393 (270 + 175)
Source: Lal et al. (1998); Follett et al. (2000); Birdsey (2000)
Table 3. Potential sink capacity of terrestrial ecosystems.
Sink capacity (Tg C/yr)
*The soil sink potential can be realized through policy intervention, and
needs to be adjusted for hidden C costs of input used.