The Societal Value of Soil Carbon Sequestration Rattan Lal Director, Carbon Management and Sequestration Center The Ohio State University, Columbus, Ohio Global Climate Change ∆T over the 20th century…………. +0.6+0.2°C Rate of ∆T increase since 1950…… +0.17°C/decade Sea level rise over 20th century….. +0.1-0.2 m Change in precipitation………….. +0.5-1%/decade Extreme events……………………. +2-4% ………..IPCC (2001) Atmospheric Concentration of Trace Gases Between 1750 and 1999 Rate of increase Radiative Gas Concentration Conc./yr forcing (w/m2) CO2 280 - 367 ppm 1.5 ppm 1.46 CH4 700 - 1745 ppb 7.0 ppb 0.48 N2O 270 - 314 ppb 0.8 ppb 0.15 CFCs 0 - 268 ppt -1.4 ppt 0.34 IPCC (2001) Global Carbon Budget Activity 1980-1989 1989-1998 -----------Pg C/y---------- A. Source Fossil fuel emission 5.0 + 0.5 6.3 + 0.6 Land us e change 1.7 + 0.8 1.6 + 0.8 B. Sink Atmosphere 3.3 + 0.2 3.2 + 0.2 Ocean 1.9 + 0.6 1.7 + 0.5 Terrestrial/missing carbon 1.9 + 1.3 2.3 + 1.3 IPCC (2001) How Much C is in Soil? (i) Soil organic C = 1550 Pg Soil inorganic C = 750 Pg Total = 2300 Pg (ii) Atmosphere = 720 Pg (iii) Biota = 560 Pg (iv) Ocean = 38,000 Pg • SOC pool = 40 - 100 Mg/ha Soil vs. Atmospheric C 1 Pg (billion tonnes) of soil C = 0.47 ppm of CO2 Mean Residence Time of C in Different Pools The average atom of C spends about: • 5 yrs in the atmosphere, • 10 yrs in vegetation (including trees), • 35 yrs in soil, and • 100 yrs in the sea. Residence time = pool / flux The residence time is longer in soils of high latitude. ra Effects of Soil Erosion and Redistribution on Trace Gases Emissions. CO2 CO2 CH4 N2O Depressed CH4 N2O oxidation of CH4 C burial Erosion C burial Redistribution DOC Depression Soil erosion and C emission Land Area Emission Reference (Mha) (Pg C/ yr) World cropland 1500 0.32 Jacinthe & Lal (2001) World soils 13,048 1.1 Lal (1995) 1.14 x 1015 g/yr decomposition 1500 x 1015 and emission to C C in world the atmosphere 3.99 x 1015 g/yr stored sequestratio soil within the terrestrial n ecosystem 5.7 x 1015 g/yr C displaced due to erosion 0.57 x 1015 g/yr transported to the ocean Global soil erosion and dynamics of soil organic carbon (Lal, 1995). Historic Soil C Loss World soils…….. 66-90 Pg U.S. soils……….. 5 Pg Recoverable C…. 50-75% Time horizon……25-50 yrs The magnitude of soil C loss 30-40 Mg/ha Agricultural soils now contain lower SOC pool than their potential, and thus have a C sink capacity. Anthropogenic emissions (1850-2000) 1. Fossil fuel: 270 + 30 Pg 2. Land use change: 136 + 55 Pg Soil: 78 + 12 Soils and Global Warming Can we use soils and vegetation for scrubbing a dirty atmosphere? Carbon Sequestration It is the net removal of CO2 from the atmosphere into the long-lived pools of C such as vegetation and soil by biotic and abiotic processes. A New Definition of Agriculture It is an anthropogenic manipulation of carbon through: uptake, fixation, emission and transfer. CU + CF = CE + CT How to Increase Soil C A. Increase (i) density of C in the soil (ii) depth of C in the profile B. Decrease (i) decomposition of C (ii) losses due to erosion Increasing Density of C in Soil Plow No till Residue removed Residue return Bare fallow Cover crops Low input Judicious input (precision farming, IPM) No water control Water conservation and supplemental irrigation Fence to fence cropping Forestation/vegetation on marginal lands/CRP Disposition of Organic Residues CO2 60-80% Organic residues 100 grams 3-8% 3-8% 10-30% Biomass Nonhumic Complex (soil organisms) compounds humic (polyuronides, compounds acids, etc.) Humus 10-35% Mulch Rate and SOC Content in Ohio No till: SOC (Mg ha-1) = 15.2 + 0.321 M R = 0.68 Plow till: SOC (Mg ha-1) = 11.9 + 0.266 M R = 0.72 Cover Crop and SOC Pool in a Miamian Soil in Ohio Treatment SOC (0-30 cm) Relative SOC Kg/m3 (5 yr) Continuous corn 2.30 100 Corn-soybean 2.34 102 Continuous soybean 2.37 103 Corn-soybean-wheat 2.36 103 Alfalfa 2.33 101 Birdsfoot trefoil 2.45 107 White clover 2.36 103 Kentucky blue grass 2.28 103 Tall fescue 2.72 118 Smooth bromegrass 2.75 120 Fallow 2.58 112 Lal (1998) SOC pool in 0-30 cm depth over a 60-year period at Coshocton, OH (Hao, Lal, Owen, 2002) Management SOC pool Rate (Mg C/ha) (Kg C/ha/yr) Conventional tillag e 24.5 -- Conventional tillag e-rotation 29.7 87 Chisel tillage (C-S) 32.1 127 No tillage (C-S) 36.8 205 No tillage (C-C) 39.6 252 No tillage (C-C)+manure 65.5 683 Biofuel vs. Fossil Fuel 1 gallon of biofuel = 0.5 gallon of oil/diesel saving Global Cooling Potential GCP = (GWP)-1 • Conservation tillage 100-1000 • Cover crops Kg C/ha/y • Nutrient management • Soil restoration • CRP/WRP • Land use and afforestation Land Use and Soil C Sequestration in the U.S. Land use Area Net potential Mha MMTC/yr Cropland 156.9 75-208 Grazing land 285.9 81-91 Forest land 236.1 49-186 CRP 13.8 9.7-14.6 WRP 0.6 0.5-0.9 Urban 20.6 2.2-8.6 Total 713.9 154-509 (332) U.S. Emissions and Soil C Sequestration • Total U.S. gas emissions……………….1500 MMTC/yr • Emission from agricultural activities…133 MMTC/yr • Net soil C sequestration potential……..332 MMTC/yr Agricultural Soils and Mitigation of GHE 1 bbl of diesel = 220 L 1 L of diesel = 0.73 Kg C 1 ton of C = 1370 L of diesel = 6.2 bbl of diesel C sequestration potential of ag soils = 2 billion barrels/yr Potential of Global Soil C Sequestration 1-2 Pg C/yr or 24% of the total emissions by fossil fuel combustion. Is Soil C Sequestration A Free Lunch? • Not really! • Additional N, P, S etc. are needed for humification of residue C. • There are hidden C costs of RMPs. Building Blocks of Humus • C is only one of several constituents of humus. • Other constituents are H, O, N, P, S and micronutrients. Nutrients Needed for Humification • How much N, P and S are needed to convert residue into humus? • How to adjust fertilizer use for desired productivity and converting residue into humus? Elemental Composition of Humus and Crop Residues Ratio Humus Crop Residue C:N 10-15 70-100 C:P 40-60 200-400 C:S 60-80 400-800 Additional Nutrients Required to Convert 10,000kg of Carbon into Humus Nutrient Quantity needed (kg) N 833 P 200 S 143 Energy-based Input and C Sequestration 1. What is the carbon budget in relation to: (i) Fertilizer use (ii) Manure application (iii) Tillage practices (iv) Irrigation (v) Liming of acid soils 2. C sequestration occurs only if output > input. Hidden C costs of tillage methods Method Kg C/ha/yr Conventional tillage 62-72 Minimum tillage 40-45 No tillage 20-23 Hidden C cost of fertilizers Fertilizer type Kg C/kg of fertilizer Nitrogen 0.86 P2O5 0.17 K2O 0.12 Lime 0.0.36 Hidden C cost of pesticides Pesticide Kg C/kg of pesticide Herbicides 4.7 Fungicides 5.2 Insecticides 4.9 Hidden C cost of irrigation Method Kg C/ha/yr Pump 140-160 Gravity 0 Farming Carbon 1. Commodification of C (price) 2. Incentives Societal Value of Carbon Nutrients and H2O contained in 1 kg of humus = $0.2 Rational price = $200/ton Undervaluing a Commodity Undervaluing carbon has and will perpetuate its misuse. Cumulative C sequestration (M/ha) 40 30 20 10 0 0 10 20 30 40 50 Time after conversion (yrs) Economics of C Sequestration 1. Assessing economics of C by itself is not adequate. 2. Evaluate the entire package of benefits: (i) To the farmer (ii) To the society Can soil C sequestration mitigate the greenhouse effect? Dependency on Carbon Modern civilization is hooked on carbon. It needs rehabilitation, in a big way. Role of soil and biomass C in global C management. Source: The Global Energy Technology Strategy, Battelle, Washington, D.C., 1998 Soil C Sequestration • It is a:Development challenge in the tropics and sub-tropics. • Policy reform and implementation challenge in developed countries. A Bridge to the Future • C sequestration in soil and vegetation is a bridge to the future. • It buys us time while alternatives to fossil fuel take effect. • It is a good thing to do, regardless of what happens to the climate. It is truly a win-win strategy.
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