Soil Carbon Sequestration for Climate Change Mitigation and Food ...

Soil Carbon Sequestration for Climate Change Mitigation and Food ...

Platinum Jubilee Celebrations of the Indian Society of Soil ScienceSouvenir, pp 39-46Soil Carbon Sequestration for Climate Change Mitigationand Food SecurityR. LalCarbon Management and Sequestration Center, Ohio State University, Columbus, OH 43210, USAIntroductionImportant among inter-related issues of globalsignificance are: (i) climate disruption, (ii) foodinsecurity, (iii) environmental degradation includingdesertification, and (iv) energy crisis. These areamong inter-twined global scale challenges drivenby anthropogenic perturbances (Walker et al., 2009)(Figs. 1 and 2). All these four issues are driven by theincrease in World’s population, which is 6.7 billionin 2009 and may increase to 9.2 billion by 2050. It isthe strong reliance on fossil fuel which is responsiblefor drastic increase in atmospheric concentration ofCO 2 and other greenhouse gases (GHGs). Sources ofall GHGs are fossil fuel combustion, cementmanufacture, deforestation along with biomassburning and soil cultivation, nitrogenous fertilizerapplication, drainage of peatlands and extractivefarming practices. Two principal sources ofanthropogenic emissions are: (i) fossil fuelcombustion and cement manufacture estimated at ~8Pg C/yr, and (ii) change in land use, drainage ofpeat lands and soil cultivation estimated at 1.6 PgC/yr (IPCC, 2007). Principal sinks of CO 2 includeuptake by the atmosphere (3.3 Pg C/yr), ocean (2.2Pg C/yr), vegetation (1.5 Pg C/yr) and land-basedsinks (2.6 Pg C/yr) (Normile, 2009; IPCC, 2007).There are numerous uncertainties in these estimates,especially about the sinks. It is difficult to quantifyhow much C is going and where. Similarly, there areuncertainties about the magnitude of emissionsthrough deforestation and land use conversion.These estimates could be off by as much as 100%(Normile, 2009).Concentration of CO 2 in the atmosphere hasincreased from 280 ppm in the pre-industrial era(~1750) to 385 ppm in 2009 (Normile, 2009), and ispresently increasing at the rate of about 2 ppm/yr(0.50 %/yr) (WMO, 2008). Atmospheric concentrationof CH 4 has increased from the pre-industrial level of700 ppb to 1789 ppb, at the rate of 13 ppb during thelate 1980s, and 6 ppb from 2006 to 2007 (0.34%/yr).Similarly, the concentration of N 2 O has increasedfrom 270 ppb in pre-industrial era to 321 ppb in 2007,and is increasing at the rate of 0.8 ppb/yr (0.25%/yr)(WMO, 2008). Because of the increase inconcentration of GHGs, mean earth’s temperaturehas already increased by 0.6 ± 0.2 °C, and is projectedto increase by 2 to 4 °C towards the end of the 21 stFig. 1. Emerging global issues of the 21 st century drivenby high demographic pressure and increasingdemands on natural resourcesFig. 2. Everything is connected to everything else

40 Platinum Jubilee Celebrations of the Indian Society of Soil Science [Dec. 22 - 25,Fig. 3. Convergence of climate disruptions, increase indemand, emphasis on biofuels and decline inagricultural production on food securitycentury under the business as usual scenario (IPCC,2007). With projected climate change, there are likelyrisks of increase in frequency and intensity of extremeevents (e.g., drought), decrease in rainfalleffectiveness, increase in incidence of pests andpathogens, reduction in net primary productivity(NPP), and decrease in crop yield and agronomicproduction.The issue of food-insecurity is stronglyintertwined with that of the climate disruption andother anthropogenic perturbations of naturalecosystems (Fig. 3). In broader terms, food insecurityinvolves low agronomic production, lack of access tofood caused by poverty, nutritional inadequacy andlow safety, and inability to utilize food because ofpoor health. Climate disruption affects agronomicproduction through adverse changes in temperatureand precipitation which alter the growing seasonduration, affect intensity and frequency of droughtand other extreme events, exacerbate incidence ofpests and pathogens, and increase magnitude ofbiotic and abiotic stresses. Demand on biofuels,driven by an insatiable need for energy, is stronglyimpacting prices of food staples (e.g., corn, soybean).Indeed, agro-fuels may exacerbate food priceinstability and worsen food insecurity for poorpeople throughout the world (Koning and Mol, 2009).The objective of this article is to review the foodinsecurityhotspots of the world, discuss the impactof projected climate change, and outline the role ofsoil C sequestration (SCS) in advancing food securitywhile mitigating the climate change.Global Hot Spots of Food InsecurityNumber of food-insecure people in the worldhas increased to 1020 million (FAO, 2009), and theU.N. Millennium Development Goals of cuttinghunger to half by 2015 will not be met. Increase inprices of food staples in 2007-08 has reduced theaccess to food and exacerbated food insecurity forpoor people around the world. Over and above theproblem of access to food, the supply of food is alsolimited by soil degradation, especially that causedby accelerated erosion, nutrient deficiency, and thedepletion of soil organic carbon (SOC) pool. Regionswith a severe problem of food insecurity includeSouth Asia (or SA comprising of Afghanistan,Pakistan, India, Nepal, Bhutan, Bangladesh and SriLanka) (FAO, 1996; Banik, 2007; Agarwal et al., 2009),and Sub-Saharan Africa (SSA) (Anonymous, 2009).Farmers in SA and SSA are small landholders,resource-poor and highly vulnerable to climaterelatedand other natural and anthropogenicdisruptions. The data in Table 1 indicate per capitacereal production in several regions of SA and SSAin 2007 and the projected per capita cerealproduction in 2030, along with the per capitacropland area harvested in 2007. The subsistencelevel threshold of per capita availability of cereals is190 kg ha -1 (Funk and Brown, 2009). With thiscriterion, those regions which will face a seriouschallenge of food-insecurity through 2030 andbeyond, are SA and the entire continent of SSA(Table 1). Whereas the per capita food productionwill decline in all regions of SA, the production isbelow the threshold optimum in Western Asia (160kg/person) and SA (193 kg/person). Assuming thataccess to food through better income can make amajor impact in reducing regional and local foodproduction gaps, food insecurity is not an issue inWestern Asia because of the oil-based revenue.However, food-insecurity will remain a serious issuein SA. By 2050, the number of food-insecure peoplein SA may increase to 373 million, and the per capitaproduction levels may reach similar to those of the1960s and 1970s (Funk and Brown, 2009). Theproblem of food-insecurity is even more daunting inSSA where the per capita cereal production is belowthe threshold level (190 kg/person) in 2007 and isprojected to decrease more drastically by 2030 (Table1). The problem may be exacerbated by the projectedclimate change and the increase in drought stress(Verhagen et al., 2004), and the attendant increase inrisks of soil degradation and land desertification.Strategies of Advancing Food Security whileMitigating Climate ChangeImproving agricultural production is the basicstrategy for both advancing food security andmitigating climate change. Indeed, agriculture mustbe the engine of economic development in SA, SSA,

2009] Soil Carbon Sequestration 41Table 1. Per capita cereal production in 2007 and 2030 in different regions of Asia and the World (Modified fromFunk and Brown, 2009)Region Per Capital Cereal Production (kg ha -1 ) Per Capita Cropland Area (ha)2007 2030 2007World 354 306 0.11North America 1374 1236 0.23AsiaEastern Asia 314 276 0.06Southern Asia 231 193 0.09South-Eastern Asia 368 356 0.10Western Asia 204 160 0.10Central Asia 541 - 0.32Sub-Saharan AfricaEastern Africa 131 84 0.09Middle Africa 62 38 0.06Northern Africa 190 180 0.11Southern Africa 182 189 0.07Western Africa 189 166 0.16and elsewhere in the developing world. It is difficultto achieve poverty reduction without priorinvestment in agriculture (Lipton, 2005), especiallyin countries where majority of the population is ruraland is dependent on agriculture. Developingcountries in SA, SSA and elsewhere may not be ableto advance economically and industrially withoutreplacing extractive and subsistence farming (Katers,2000; Funk and Brown, 2009) by science-basedagriculture comprising of proven technologies andrecommended management practices (RMPs). Inaddition to advancing food security and alleviatingpoverty, raising low crop yields, and breaking theagronomic barriers in SA and SSA (especially inrainfed/dry farming agroecosystems), SCS may alsobe the judicious strategy to adapt to climate change.The fact is that even the modest increase (20% to30%) in production in rainfed agriculture in SA andSSA through SCS can have a drastic positive impacton the standard of living and wellbeing of hundredsof millions of people now living below the povertyline.Adaptation to Climate ChangeStrategies for adaptation to climate change,reducing risks to agriculture by adverse changes ingrowing season through alterations in precipitationand temperature regimes, are different at farm,national and global scales (Fig. 4). At the farm level,the goal is to improve soil quality and adjust farmingoperations to buffer against the adverse effects ofclimatic disruption. Improvements in soil quality canbe brought about by RMPs of soil management suchas mulch farming (Acharya and Sharma, 1994),conservation agriculture (Acharya et al., 1998),integrated nutrient management (INM), waterharvesting and recycling through drip sub-irrigation(DSI) and judicious landscape management.Increasing fertilizer/N use efficiency, which in Indiadecreased from 60 kg grain/kg of N applied in 1980to 25 kg grain/kg of N applied in 2005 (IFA, 2007), isessential to increasing crop yields per unitconsumption of energy-based inputs. Replacement offlooded rice by aerobic rice is important for savingwater and sustaining crop yields (Kreye et al., 2009;Bouman et al., 2007; Ladha et al., 2009). Applicationof biosolids as soil amendments (e.g., compost,manure) is extremely important to improvingproductivity (Bejbaruha et al., 2009), and creating apositive C budget and enhancing the ecosystem Cpool. Growing improved varieties (including GMcrops) and selecting alternate crops which creatediverse cropping/farming systems are essential toenhancing soil resilience. Climate change will createnumerous opportunities of growing alternate crops,and availing such an opportunity can improvehousehold income, enhance production, and increaseaccess to food.There are essential conditions of enhancingadaptation to climatic disruption at the nationallevel. Important among these are political, economicand social stability, investments in agriculture,strengthening institutional support, and improvingaccess to market and credit. At the global scale, thestrategy is to restore degraded soils and desertifiedecosystems, create opportunities for cleandevelopment mechanisms (CDM), formulate andimplement World Soil Policy, and enhance ecosystemresilience (Fig. 4). It is important to commoditize soilC, so that it can be traded as any other farmcommodity. It is better to reward farmers fordelivering ecosystem services (e.g., C sequestration,

42 Platinum Jubilee Celebrations of the Indian Society of Soil Science [Dec. 22 - 25,Fig. 4. Strategies for adaptation to climate changewater quality improvement, biodiversity enhancement)than to provide subsidies, and give emergenceaid as handouts.Soil Carbon Sequestration to MitigateClimate ChangeWorld soils comprise the third largest globalpool after the oceanic pool of 38000 Pg, the geologic/fossil C pool of ~5000 Pg. The soil C pool is estimatedat 2500 Pg, which has two distinct but relatedcomponents: (i) the soil organic carbon (C) pool ofabout 1550 Pg, and (ii) the soil inorganic carbon(SIC) pool of about 950 Pg. Estimated to 1-m depth,the total soil C pool of about 2500 is about 3.2 timesthe atmospheric pool of 780 Pg, 40 times the bioticpool of 620 Pg, and about 1.8 times the terrestrialpool of 1400 Pg which is equal to combinedatmospheric and biotic pools together. Theatmospheric pool is increasing annually at the rateof 3.3 Pg C/yr (WMO, 2008; IPCC, 2007), while theterrestrial pool is decreasing because ofdeforestation, biomass burning, soil cultivation anddrainage of wet/peat lands. There is a direct linkbetween the soil and the atmospheric C pools, 1 Pgof soil C pool is equivalent to 0.47 ppm of CO 2concentration in the atmosphere, and vice versa.Conversion of natural and agriculturalecosystems leads to decline in the terrestrial (bioticand soil C) pools. The decline is caused by removalof the perennial vegetation cover (e.g., trees, shrubs,grasses) by seasonal/annuals which have low NPP.Thus, the amount of biomass-C returned to the soil islower in agricultural than natural ecosystems.Furthermore, soils under agricultural ecosystemshave higher decomposition rate than those undernatural vegetation because of differences in soiltemperature and moisture regimes. The rate ofdepletion of the SOC pool in agricultural ecosystemsis exacerbated by soil degradation processes such asaccelerated erosion by water and wind. Excessivetillage and drainage accentuate the rate of SOMdecomposition. The rate and magnitude of depletionof SOC pool are also accentuated by removal of cropresidues and uncontrolled grazing. Thus, mostagricultural soils have lower SOC pool than theircounterparts under natural ecosystems. The SOC

2009] Soil Carbon Sequestration 43pool in agricultural soils is lower than those undernatural ecosystems by 25% to 50% in temperateclimates and 50% - 75% in tropical regions (Lal,2004). Most agricultural soils have lost 30 to 40 MgC/ha, which can be restored.Therefore, conversion of degraded and depletedagricultural soils to restorative land use(s) andadoption of RMPs can restore the SOC pool. Theprocess of restoration of SOC pool, throughconversion of atmospheric CO 2 into humus viaphotosynthesis, is called soil C sequestration.Similarly, the processes of increasing the terrestrialC pool (biota and soil) through photosynthesis andincremental addition of biomass C (above and belowground)is called terrestrial C sequestration.Assuming that the SOC pool to 1-m depth canbe increased by 10% on a global scale over the next50 to 100 years, difficult and challenging as the taskmay be, transfer of 250 Pg of atmospheric C 910% of2500 Pg of soil C pool to 1-m depth) is equivalent toreducing atmospheric CO 2 concentration by 118 ppm(250 Pg x 0.47 ppm/Pg). If the process can bepresumably accomplished today (which is notpossible), increasing the soil C pool by 250 Pg woulddraw down the atmospheric CO 2 concentration from383 ppm to 265 ppm, which is even lower than thepre-industrial concentration of 280 ppm. Indeed Csequestration in terrestrial ecosystems (soils andtrees) is the only cost-efficient process of reducingthe atmospheric abundance of CO 2 (McKinsey & Co.,2009). The best one can hope to achieve with thecarbon capture and sequestration (CCS or geologicsequestration), is to stabilize the atmosphericconcentration with 100% efficiency. In most cases,the efficiency of CCS with 15% additional cost ofgenerating electricity is about 30%.Ever since the dawn of settled agriculture about10 millennia ago, the terrestrial ecosystems have lostas much as 478 Pg of C (Ruddiman, 2007; IPCC,2007). Even if two-thirds of this can be restored(through afforestation, soil amelioration, andrestoration of wetland/peat soils by inundation),this means increasing the terrestrial C pool by ~320Pg or the equivalent to draw down the atmosphericCO 2 by 150 ppm.These estimates of 120 to 150 ppm of drawdown of atmospheric CO 2 are indicative of thetechnical potential of the strategy of C sequestrationin terrestrial ecosystems. The attainable andeconomic potentials are much lower and depend onthe site specific and regional conditions. The rate ofC sequestration in terrestrial ecosystems is 3-4 Pg C/yr until 2050 (Pacala and Socolow, 2006) throughadoption of no-till farming and conservationagriculture, afforestation, and establishment ofenergy plantations.Co-benefits of Soil Carbon SequestrationSequestration of atmospheric CO 2 into theterrestrial ecosystems in general and soils inparticular, is a win-win-win strategy. Amongnumerous co-benefits are: (i) advancing food securitythrough improvements in soil quality, (ii) restoringdegraded soils and desertified ecosystems, and (iii)mitigating climate change while improving theenvironment. It is extremely important to realize thatenhancing SOC pool and maintaining it above thethreshold (1.1% in the surface layer, Aune and Lal,1998) is essential to advancing food security. Formalnourished and resource-poor small landholderswho are perpetually threatened by drought and cropfailure, enhancing soil resilience and guaranteeing aminimum assured crop yield even during the worstseasons of below-normal rains is important to theirsurvival. Thus, soil C sequestration is essential totheir survival. Rather than being driven into thefutile debate of who is responsible for gaseousemissions, food-insecure population wouldappreciate C-positive action towards elimination ofhunger and malnutrition for which soil Csequestration is an important step and in the rightdirection. Commoditization of soil C can also createanother income stream and provide the much-neededincentives for adoption of RMPs. Land managers canbenefit by trading soil C in the emerging C-offsetmarkets and by claiming the environmental benefitsof the sustainable land management practices.Similar to C, the farmers can also be paid for watermanagement. Downstream farmers may be requiredto pay upstream land managers for specific practiceswhich ensure availability of good quality water.Payments for green water credits and charging usersa fair price of the scarce water resource may be theonly strategy to reverse the severe depletion of theground water resources in northern India, as hasbeen reported by Kerr (2009), Rodell et al. (2009). Bothwater credits and C credits are important to adoptionof RMPs, and sustaining the resource use.Sustainable crop management is important toalleviating poverty (Lipton, 2005). Furthermore, thiscost-effective option of mitigating climate change isalso a bridge to the future until C-neutral or C-negative fuel sources take effect.Diffusing the Population Bomb throughImprovement in AgricultureThe world population has doubled numeroustimes since the primate started walking on two feetand descended from their habitat in trees. It was

44 Platinum Jubilee Celebrations of the Indian Society of Soil Science [Dec. 22 - 25,merely 5 million around 8,000 BC, 10 million in 3500BC, 50 million by 1250, 800 million by 1750 and 1650million by 1900. It has doubled twice during the 20 thcentury to 6.7 billion in 2009. World population isexpected to stabilize at ~10 billion around 2100, andwill, thus, never double again. Evolution ofagriculture about 10,000 years ago and its scientificadvances especially during the 20 th century havebeen responsible for increase in population.However, the future increases in population will alsobe moderated by improvements in agriculturalproduction. Just as the quantum jump in agronomicproduction by The Green Revolution saved billionsfrom hunger and malnutrition. Similarly, usingimproved agriculture as the engine of economicdevelopment in Africa and Asia would dampen therate of population growth and stabilize worldpopulation lower than the 10 billion mark (6 or 7billion by 2200 and beyond). Advancing foodsecurity, enhancing income, and improvingstandards of living are essential to reducing the rateof population growth. It is in this regard that theimportance of improving soil quality and increasingagronomic production cannot be over-emphasized.Managing Carbon-Climate Risks through SoilSequestrationTwo strategies of managing risks of climatechange are: (i) reducing anthropogenic emissions,and (ii) sequestering emissions. Reducinganthropogenic emissions is the best strategy of whichidentifying low-C or no-C fuel sources and improvinguse efficiency of power are among numerous options.Sequestering emissions through the natural processof photosynthesis, and humification of biomass isthe next best option and is a priority consideration.Carbon capture and storage (Chu, 2009; Schrag, 2009;Orr, Jr., 2009; Rochelle, 2009; Hazzeldine, 2009;Normile, 2009) is of a lesser importance, especiallywhen the first two options are judiciously andprudently implemented. While soil C sequestrationis not a silver bullet for mitigating climate change, itis essential for numerous co-benefits which areimportant to human wellbeing and other ecosystemservices. These co-benefits are illustrated in Figure 5.It is these co-benefits of soil C sequestration whichare important consideration in choosing it as astrategy for managing carbon-related climate risks.Resource-poor farmers and food-insecure people caremore about increase in agronomic production andminimum assured crop yields through improvementsin soil quality than the potential of mitigating climatechange. Improvements in the quantity and quality ofrenewable fresh water resources are anotherimportant co-benefit of C sequestration in soils andterrestrial ecosystems. Establishment of energyplantations, especially on degraded croplands andother lands of marginal soil quality can also enhanceecosystem services from land of otherwise low utility.Tenets of Soil ManagementSoils must never be taken for granted. Soilsmust be used, improved and restored for generationsto come. Sustainable management of soils is essentialthrough observing 10 tenets of soil management (Lal,2009a; b; Fig. 5). Ten tenets of soil management,constituting as spokes of a wheel representing theecosystem services, include the following: (i) soildegradation by biophysical processes is driven bysocial, economic and political forces, (ii) desperateand helpless people do not care for the stewardship,(iii) to be sustainable, all outputs must be balancedby equivalent inputs in terms of nutrients andcarbon, (iv) poor soils make people poor, and poorpeople make soils worst, (v) plants cannotdifferentiate between organic and inorganic sourcesof nutrients, and it is a matter of logistics and accessto supply nutrients to crop at the most critical stagesand for the amount required, (vi) soils can be a sourceor sink of atmospheric CO 2 depending on land useand management, (vii) a perpetual and widespreaduse of extractive farming practices can degrade thesoils and the environment, (viii) benefits of improvedvarieties and GM crops can only be realized whengrown under optimal soils and agronomicconditions, (ix) improved agriculture is a solution(rather than a cause) of the environmental problem,and (x) adoption of modern innovations of soilmanagement, built upon the traditional knowledge,is essential to addressing the global issues.Fig. 5. Co-benefits of carbon sequestration in soils andterrestrial ecosystems

2009] Soil Carbon Sequestration 45Fig. 6. Ten tenets of soil management (Adapted from Lal, 2009b).ConclusionsSoils provide numerous ecosystem servicesessential to well being of all planetary life. Importantamong these are: producing biomass, cyclingelements, denaturing and transforming of pollutants,purifying and filtering of water, storing and creatinghabitat for a vast gene pool, providing foundationsfor civil structures, generating raw materials, andserving as an archive of planetary and humanhistory. Soil’s capacity to provide these servicesdepends on its quality (physical, chemical andbiological) as moderated by the total and reactivecarbon (C) pools. Most agricultural soils containlower organic C (SOC) pool than their counterpartsunder natural ecosystems by about 25% to 50% intemperate and 50% to 75% in tropical ecosystems.The magnitude and severity of the depletion of SOCpool are exacerbated through decline in soil qualityby accelerated erosion and other degradationprocesses. Perpetual use of extractive farmingpractices and mining of soil fertility also deplete theSOC pool. Conversion to a restorative land use andadoption of recommended management practices(RMPs), which create positive C and nutrient (N, P,K, S) budgets, can enhance SOC pool while restoringsoil quality. The rate of SOC sequestration in soils ofthe terrestrial ecosystems is 2-3 Pg C/yr. IncreasingSOC pool is also essential to advancing food securityand improving ecosystem services. Adoption ofRMPs by the resource-poor farmers can be promotedby payments for soil C credits, green water credits,and biodiversity credits. In addition to mitigation ofclimate change, soil C sequestration is also importantfor adaptation to climate disruption by bufferingagricultural ecosystems against adverse changes intemperature, precipitation and other extreme events.Soil carbon sequestration is a win-win-winstrategy. Through its numerous co-benefits, itmitigates climate disruption, adapts agroecosystemsto climate change, advances food security, andimproves the environment. Rather than subsidiesand emergency aids, payments to land managers forC credits, green water credits, and biodiversitycredits can promote adoption of recommendedmanagement practices. This is a cost-effectivestrategy of moderating climate change, and is theonly natural and viable option of reducing theatmospheric abundance of CO 2 . The drawdownpotential of soil C sequestration will help reducingatmospheric CO 2 concentration by 120 to 150 ppmover the next 50-100 years, while ensuring the foodsecurity for 10 billion people and improving theenvironment.

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