1. Estimated Increase in Atmospheric CO 2 due to Worldwide Decreases in Soil Organic Matter R.W. Mullen, W.E. Thomason, and W.R. Raun R.W. Mullen, W.E. Thomason, and W.R. Raun

2. IntroductionIntroduction Atmospheric CO 2 has increased over the last 150 years from 260 to 340 mg kg -1 (360) Atmospheric CO 2 has increased over the last 150 years from 260 to 340 mg kg -1 (360) Expected to rise 1.5 to 2.0 ppm per year (Wittwer, 1985) Expected to rise 1.5 to 2.0 ppm per year (Wittwer, 1985) Responsible for 0.5 °C global temp increase Responsible for 0.5 °C global temp increase Increasing atmospheric CO 2 is due to industrial burning of fossil fuels and changing land use (deforestation and cultivation) Increasing atmospheric CO 2 is due to industrial burning of fossil fuels and changing land use (deforestation and cultivation) Benefits associated with increased atmospheric CO2 (increased water use efficiency, nitrogen use efficiency and production in many crops) Benefits associated with increased atmospheric CO2 (increased water use efficiency, nitrogen use efficiency and production in many crops) Atmospheric CO 2 has increased over the last 150 years from 260 to 340 mg kg -1 (360) Atmospheric CO 2 has increased over the last 150 years from 260 to 340 mg kg -1 (360) Expected to rise 1.5 to 2.0 ppm per year (Wittwer, 1985) Expected to rise 1.5 to 2.0 ppm per year (Wittwer, 1985) Responsible for 0.5 °C global temp increase Responsible for 0.5 °C global temp increase Increasing atmospheric CO 2 is due to industrial burning of fossil fuels and changing land use (deforestation and cultivation) Increasing atmospheric CO 2 is due to industrial burning of fossil fuels and changing land use (deforestation and cultivation) Benefits associated with increased atmospheric CO2 (increased water use efficiency, nitrogen use efficiency and production in many crops) Benefits associated with increased atmospheric CO2 (increased water use efficiency, nitrogen use efficiency and production in many crops)

3. IntroductionIntroduction The amount of carbon released by industrial processes and changing land use was estimated to be 5.0 x 10 12 and 2.0 x 10 12 kg C yr -1, respectively The amount of carbon released by industrial processes and changing land use was estimated to be 5.0 x 10 12 and 2.0 x 10 12 kg C yr -1, respectively Carbon can be sequestered by the crop-root system and redistributed deeper into the soil profile, making it less likely to be converted back to CO 2 Carbon can be sequestered by the crop-root system and redistributed deeper into the soil profile, making it less likely to be converted back to CO 2 The amount of carbon released by industrial processes and changing land use was estimated to be 5.0 x 10 12 and 2.0 x 10 12 kg C yr -1, respectively The amount of carbon released by industrial processes and changing land use was estimated to be 5.0 x 10 12 and 2.0 x 10 12 kg C yr -1, respectively Carbon can be sequestered by the crop-root system and redistributed deeper into the soil profile, making it less likely to be converted back to CO 2 Carbon can be sequestered by the crop-root system and redistributed deeper into the soil profile, making it less likely to be converted back to CO 2

4. Conventional tillage practices (moldboard plow, disk harrow, chisel plow, etc.) can release carbon as CO 2 via the accelerated decomposition of soil organic matter Conventional tillage practices (moldboard plow, disk harrow, chisel plow, etc.) can release carbon as CO 2 via the accelerated decomposition of soil organic matter Organic Matter decomposition = global warming Organic Matter decomposition = global warming Conventional tillage practices (moldboard plow, disk harrow, chisel plow, etc.) can release carbon as CO 2 via the accelerated decomposition of soil organic matter Conventional tillage practices (moldboard plow, disk harrow, chisel plow, etc.) can release carbon as CO 2 via the accelerated decomposition of soil organic matter Organic Matter decomposition = global warming Organic Matter decomposition = global warming IntroductionIntroduction

6. ObjectiveObjective The objective of this work was to derive a simple estimate of CO 2 in the atmosphere that could be attributed to tillage and decomposition of soil organic matter. The objective of this work was to derive a simple estimate of CO 2 in the atmosphere that could be attributed to tillage and decomposition of soil organic matter.

7. DiscussionDiscussion Soil organic matter has declined in agricultural soils largely due to cultivation (Boman et al., 1996 and Reicosky, 1994). Soil organic matter has declined in agricultural soils largely due to cultivation (Boman et al., 1996 and Reicosky, 1994). Estimates of soil organic matter loss since initial cultivation range from as low as 20% (Schlesinger, 1986) to as high as 54% (Smith et al., 1997). Estimates of soil organic matter loss since initial cultivation range from as low as 20% (Schlesinger, 1986) to as high as 54% (Smith et al., 1997). Native prairie soils in the Central Great Plains contained 4% soil organic matter in the 1800s, and after more than 150 years of cultivation that number is now less than 1% (Boman et al., 1996). Native prairie soils in the Central Great Plains contained 4% soil organic matter in the 1800s, and after more than 150 years of cultivation that number is now less than 1% (Boman et al., 1996). Soil organic matter has declined in agricultural soils largely due to cultivation (Boman et al., 1996 and Reicosky, 1994). Soil organic matter has declined in agricultural soils largely due to cultivation (Boman et al., 1996 and Reicosky, 1994). Estimates of soil organic matter loss since initial cultivation range from as low as 20% (Schlesinger, 1986) to as high as 54% (Smith et al., 1997). Estimates of soil organic matter loss since initial cultivation range from as low as 20% (Schlesinger, 1986) to as high as 54% (Smith et al., 1997). Native prairie soils in the Central Great Plains contained 4% soil organic matter in the 1800s, and after more than 150 years of cultivation that number is now less than 1% (Boman et al., 1996). Native prairie soils in the Central Great Plains contained 4% soil organic matter in the 1800s, and after more than 150 years of cultivation that number is now less than 1% (Boman et al., 1996).

8. For this work, a 3% loss in organic matter from arable soils worldwide was assumed. For this work, a 3% loss in organic matter from arable soils worldwide was assumed. DiscussionDiscussion

9. Weight of 1 hectare of soil to a depth of 15 cm (soil bulk density of 1.49 Mg/m 3 ) 2 235 000 kg ha -1 2 235 000 kg ha -1 10 000 m 2 * 1.49 Mg m -3 * 0.15 m Organic carbon lost 1.47% 1.47% Organic carbon = (organic matter – 0.35)/1.8 (Ranney, 1969) Carbon lost from organic matter per hectare 32 845.5 kg ha -1 32 845.5 kg ha -1 2 235 000 kg ha -1 * 0.0147 Arable land in the world 1 381 917 000 ha 1 381 917 000 ha www.fao.org, 1996 Total carbon lost from all arable land in the world 4.55 x 10 13 kg 4.55 x 10 13 kg 32 845.5 kg ha -1 * 1 381 917 000 ha 60% of carbon lost from organic matter converted to CO 2 2.73 x 10 13 kg 2.73 x 10 13 kg 4.55 x 10 13 kg * 0.60 (Brady and Weil, 1996) Total CO 2 lost to the atmosphere 1.00 x 10 14 kg 1.00 x 10 14 kg 2.73 x 10 13 kg * 3.67 ((44 g/mol CO 2 )/(12 g/mol C)) Mass of Earth's Atmosphere 5.00 x 10 18 kg 5.00 x 10 18 kg Wild, 1993 Change in atmospheric CO 2 0.008% 0.008% 80 mg kg -1 (Lal et al., 1997) change in CO 2 /10 000 Increase in atmospheric CO 2 4.00 x 10 14 kg 4.00 x 10 14 kg 5.00 x 10 18 kg * 0.00008 Change in atmospheric CO 2 due to organic matter decay 25.03% 25.03% 1.00 x 10 14 kg/400 x 10 14 kg Increase in atmospheric CO 2 due to 3% loss of organic matter worldwide 20.03 mg kg -1 20.03 mg kg -1 80 mg kg -1 * 0.2503 TABLE 1. Components used for calculating increased atmospheric CO 2 due to worldwide decreases in soil organic matter, assuming a decrease from 4% to 1% over the past 150 years on worldwide arable land.

10. Carbon lost from organic matter 48052.5 kg 48052.5 kg 6.64 x 10 13 kg (Schlesinger, 1984 and 1995) / 1 318 917 000 ha Organic carbon lost 2.15% 2.15% 48052.5 kg / 2 235 000 000 Organic carbon matter lost 4.22% 4.22% (0.0215 * 180) + 0.35 (Ranney, 1969) Total carbon lost from world 6.64 x 10 13 kg 6.64 x 10 13 kg Schlesinger, 1984 and 1995: 3.6 x 10 13 kg + (38 yrs * 8.00 x 10 11 kg) 60% of carbon lost from organic matter converted to CO 2 3.984 x 10 13 kg 3.984 x 10 13 kg 6.64 x 10 13 kg * 0.60 (Brady and Weil, 1996) Total CO 2 lost to atmosphere 1.462 x 10 14 kg 1.462 x 10 14 kg 3.984 x 10 13 kg * 3.67 Change in atmospheric CO 2 due to organic matter decay 36.55% 36.55% 1.462 x 10 14 kg/4.00 x 10 14 kg Increase in atmospheric CO 2 due to 3% loss of organic matter worldwide 29.24 mg kg -1 29.24 mg kg -1 80 mg kg -1 * 0.3655 TABLE 2. Components used for the calculating increased atmospheric CO 2 due to worldwide decreases in soil organic matter, using Schlesinger (1984 and 1995) data.

11. ConclusionConclusion The continuous tillage of arable land worldwide is likely responsible for 6 to 36% of the increase in atmospheric CO 2 due to decreased soil organic matter. The continuous tillage of arable land worldwide is likely responsible for 6 to 36% of the increase in atmospheric CO 2 due to decreased soil organic matter.