Land use change and soil organic carbon dynamics

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RESEARCH ARTICLELand use change and soil organic carbon dynamicsPete SmithReceived: 15 May 2007 / Accepted: 30 August 2007 / Published online: 10 October 2007 Springer Science+Business Media B.V. 2007Abstract Historically, soils have lost 4090 Pgcarbon (C) globally through cultivation and distur-bance with current rates of C loss due to land usechange of about 1.6 0.8 Pg C y1, mainly in thetropics. Since soils contain more than twice the Cfound in the atmosphere, loss of C from soils canhave a significant effect of atmospheric CO2 concen-tration, and thereby on climate. Halting land-useconversion would be an effective mechanism toreduce soil C losses, but with a growing populationand changing dietary preferences in the developingworld, more land is likely to be required foragriculture. Maximizing the productivity of existingagricultural land and applying best managementpractices to that land would slow the loss of, or issome cases restore, soil C. There are, however, manybarriers to implementing best management practices,the most significant of which in developing countriesare driven by poverty. Management practices thatalso improve food security and profitability are mostlikely to be adopted. Soil C management needs toconsidered within a broader framework of sustainabledevelopment. Policies to encourage fair trade,reduced subsidies for agriculture in developed coun-tries and less onerous interest on loans and foreigndebt would encourage sustainable development,which in turn would encourage the adoption ofsuccessful soil C management in developing coun-tries. If soil management is to be used to help addressthe problem of global warming, priority needs to begiven to implementing such policies.Keywords Soil organic carbon SOC Land use change Sequestration Barriers Sustainable development Climate mitigationIntroductionFactors controlling the level of soil organiccarbonThe level of soil organic carbon (SOC) in a particularsoil is determined by many factors including climaticfactors (e.g. temperature and moisture regime) andsoil-related factors (e.g. soil parent material, claycontent, cation exchange capacity; Dawson and Smith2007). For a given soil type, SOC stock can also vary,the stock being determined by the balance of net Cinputs to the soil (as organic matter) and net losses of Cfrom the soil (as carbon dioxide, dissolved organic Cand loss through erosion). Carbon inputs to the soil arelargely determined by the land use, with forest systemstending to have the largest input of C to the soil (inputsall year round) and often this material is also the mostrecalcitrant. Grasslands also tend to have large inputs,P. Smith (&)School of Biological Sciences, University of Aberdeen,Cruickshank Building, St Machar Drive,Aberdeen AB24 3UU, UKe-mail: Cycl Agroecosyst (2008) 81:169178DOI 10.1007/s10705-007-9138-ythough the material is often less recalcitrant than forestlitter and the smallest input of C is often found incroplands which have inputs only when there is a cropgrowing and where the C inputs are among the mostlabile. The smaller input of C to the soil in croplandsalso results from removal of biomass in the harvestedproducts, and can be further exacerbated by cropresidue removal, and by tillage which increases SOCloss by breaking open aggregates to expose protectedorganic C to weathering and microbial breakdown, andalso by changing the temperature regime of the soil.Rate of C input to the soil is related also to theproductivity of the vegetation growing on that soil,measured by net primary production (NPP). NPPvaries with climate, land cover, species compositionand soil type. Moreover, NPP shows seasonal variationdue to its dependence on light and temperature, e.g.broadleaf temperate forests are highly productive forpart of the year only (Malhi et al. 2002). Over longertime periods, a proportion of NPP enters the soil asorganic matter (OM) either via plant leachates, rootexudates, or by decomposition of litter and fragmentedplant structures (Jones and Donnelly 2004), where it isconverted back to CO2 and CH4 via soil (heterotrophic)respiration processes. The remaining C is termed netecosystem production (NEP). However, other pro-cesses such as harvest, fire and insect damage alsoremove C, which when combined with the heterotro-phic processes counterbalance the terrestrial CO2 inputfrom GPP. Any residual C is termed net biomeproduction (NBP) and can be negative or positivedepending on whether the terrestrial ecosystem is asource or sink for C (Cao and Woodward 1998; IGBP1998; Schlesinger and Andrews 2000; Janzen 2004;Jones and Donnelly 2004). Climate and land-use arethe main causes of temporal and spatial fluctuationsbetween these opposing fluxes. Very small C inputs tothe soil, as dissolved organic C, comes from wet, dryand occult (fog and cloud) deposition (Dawson andSmith 2007). Impacts of land use and land managementchange on SOC are discussed further below.The role of soils in the global carbon cycleGlobally, soils contain about three times the amount ofC in vegetation and twice the amount in the atmosphere(IPCC 2000a), i.e. about 1,500 Pg (1 Pg = 1 Gt =1015 g) of organic C (Batjes 1996). The annual fluxes ofCO2 from atmosphere to land (global Net PrimaryProductivity [NPP]) and land to atmosphere (respira-tion and fire) are each of the order of 60 Pg C y1(IPCC 2000a). During the 1990s, fossil fuel combustionand cement production emitted 6.3 1.3 Pg C y1to the atmosphere, whilst land-use change emitted1.6 0.8 Pg C y1 (Schimel et al. 2001; IPCC 2001).Atmospheric C increased at a rate of 3.2 0.1 Pg C y1,the oceans absorbed 2.3 0.8 Pg C y1 with an esti-mated residual terrestrial sink of 2.3 1.3 Pg C y1(Schimel et al. 2001; IPCC 2001).The size of the pool of SOC is therefore largecompared to gross and net annual fluxes of C to andfrom the terrestrial biosphere (Smith 2004). Figure 1(IPCC 2001) shows a schematic diagram of the Ccycle, with part (a) showing the main pools and flows ofthe natural global C cycle, and part (b) showing thehuman perturbation to the flows of C between thepools.Small changes in the SOC pool could havedramatic impacts on the concentration of CO2 in theatmosphere. The response of SOC to global warmingis, therefore, of critical importance. One of the firstexamples of the potential impact of increased releaseof terrestrial C on further climate change was given byCox et al. (2000). Using a climate model with acoupled C cycle, Cox et al. (2000) showed that releaseof terrestrial C under warming would lead to a positivefeedback whereby C release would result in increasedglobal warming. Since then, a number of coupledclimate carbon cycle (so called C4 models) have beendeveloped. However, there remains considerableuncertainty concerning the extent of the terrestrialfeedback, with the difference between the modelsamounting to 200 ppm. CO2-C by 2100 (Friedling-stein et al. 2006). This difference is of the same orderas the difference between fossil fuel C emissionsunder the IPCC SRES emission scenarios (IPCC2000b). It is clear that better quantifying the responseof terrestrial C, a large proportion of which derivesfrom the soil, is essential for understanding the natureand extent of the earths response to global warming.Understanding interactions between climate and land-use change will also be critically important.Historical losses of SOC due to land use changeHistorically, soils have lost between 40 and 90 Pg Cglobally through cultivation and disturbance170 Nutr Cycl Agroecosyst (2008) 81:169178123(Houghton 1999; Houghton et al. 1999; Schimel1995; Lal 1999). It is estimated that land use changeemitted 1.6 0.8 Pg C y1 to the atmosphere duringthe 1990s (Schimel et al. 2001; IPCC 2001).Land use change and soc lossLand use change significantly affects soil C stock(Guo and Gifford 2002). Most long term experimentson land use change show significant changes in SOC(e.g. Smith et al. 1997, 2000, 2001a, 2002). This islikely to continue into the future; a recent modelingstudy examining the potential impacts of climate andland use change on SOC stocks in Europe, land usechange was found to have a larger net effect on SOCstorage than projected climate change (Smith et al.2005a).In a meta-analysis of long term experiments, Guoand Gifford (2002) showed that converting forestland or grassland to croplands caused significant lossof SOC, whereas conversion of forestry to grasslanddid not result is SOC loss in all cases. Totalecosystem C (including above ground biomass), doeshowever, decrease due to loss of the tree biomassC. Similar results have been reported in Brazil, wheretotal ecosystem C losses are large, but where soil Cdoes not decrease (Veldkamp 1994; Moraes et al.1995; Neill et al. 1997; Smith et al. 1999), thoughother studies have shown a loss of SOC uponconversion of forest to grassland (e.g. Allen 1985;Mann 1986; Detwiller and Hall 1988). In the mostfavorable case, only about 10% of the total ecosystemC lost after deforestation (due to tree removal,burning etc.) can be recovered (Fearnside 1997; Neillet al. 1997; Smith et al. 1999).The largest per-area losses of SOC occur wherethe C stock are largest, e.g. in highly organic soilssuch as peatlands, either through drainage, cultivationor liming. Organic soils hold enormous quantities ofSOC, accounting for 329525 Pg C, or 1535% ofthe total terrestrial C (Maltby and Immirizi (1993),with about one fifth (70 Pg) located in the tropics.Studies of cultivated peats in Europe show that theycan lose significant amounts of SOC through oxida-tion and subsidence; between 0.8 and 8.3 t C ha1 y1(Nykanen et al. 1995; Lohila et al. 2004; Maljanenet al. 2001, 2004). The potential for SOC loss fromland use change on highly organic soils is thereforevery large.GeologicalreservoirsRockcarbonatesFossilorganiccarbonLandPlants[500]Soil[1500]SedimentOcean [38000]Atmosphere [730]Vulcanism In short, SOC tends to be lost when convertinggrasslands, forest or other native ecosystems tocroplands, or by draining, cultivating or liminghighly organic soils. SOC tends to increase whenrestoring grasslands, forests or native vegetation onformer croplands, or by restoring organic soils totheir native condition. Where the land is managed,best management practices that increase C inputs tothe soil (e.g. improved residue and manure manage-ment) or reduce losses (e.g. reduced impact tillage,reduced residue removal) help to maintain or increaseSOC levels. Management practices to increase SOCstorage are discussed in the next section.The most effective mechanism for reducing SOCloss globally would be to halt land conversion toagriculture, but with the population growing and dietschanging in developing countries (Smith et al. 2007b;Smith and Trines 2007), more land is likely to berequired for agriculture. To meet growing andchanging food demands without encouraging landconversion to agriculture will require productivity oncurrent agricultural land to be increased (Vlek et al.2004). In addition to increasing agricultural produc-tivity, there are a number of other managementpractices that can be used to prevent SOC loss. Theseare described in more detail in the next section.Land use change and land management to restoreor sequester socThe global potential for sequestration of SOCSoil C sequestration can be achieved by increasingthe net flux of C from the atmosphere to the terrestrialbiosphere by increasing global C inputs to the soil(via increasing NPP), by storing a larger proportionof the C from NPP in the longer-term C pools in thesoil, or by reducing C losses from the soils byslowing decomposition. For soil C sinks, the bestoptions are to increase C stocks in soils that havebeen depleted in C, i.e. agricultural soils anddegraded soils, or to halt the loss of C from cultivatedpeatlands (Smith et al. 2007a).Early estimates of the potential for additional soilC sequestration varied widely. Based on studies inEuropean cropland (Smith et al. 2000), US cropland(Lal et al. 1998), global degraded lands (Lal 2001)and global estimates (Cole et al. 1996; IPCC 2000a),an estimate of global soil C sequestration potential is0.9 0.3 Pg C y1 was made by Lal (2004a, b),between a 1/3 and 1/4 of the annual increase inatmospheric C levels. Over 50 years, the level of Csequestration suggested by Lal (2004a) would restorea large part of the C lost from soils historically.The most recent estimate (Smith et al. 2007a) isthat the technical potential for SOC sequestrationglobally is around 1.3 Pg C y1, but this is veryunlikely to be realized. Economic potentials for SOCsequestration estimated by Smith et al. (2007a) were0.4, 0.6 and 0.7 Pg C y1 at carbon prices of 020, 050 and 0100 USD t CO2-equivalent1, respectively.At reasonable C prices, then, global soil C sequestra-tion seems to be limited to around 0.40.7 Pg C y1.Even then, there are barriers (e.g. economic, institu-tional, educational, social) that mean the economicpotential may not be realized (Trines et al. 2006;Smith and Trines 2007). The estimates for C seques-tration potential in soils are of the same order as forforest trees, which have a technical potential tosequester about 12 Pg C y1 (IPCC 1997; Trexler1988 [cited in Metting et al. 1999]), but economicpotential for C sequestration in forestry is similar tothat for soil C sequestration in agriculture (IPCCWGIII 2007).Many reviews have been published recently dis-cussing options available for soil C sequestration andmitigation potentials (e.g. IPCC 2000a; Cannell 2003;Metting et al. 1999; Smith et al. 2000; Lal 2004a; Lalet al. 1998; Nabuurs et al. 1999; Follett et al. 2000;Freibauer et al. 2004; Smith et al. 2007a). Table 1summarizes the main soil C sequestration optionsavailable in agricultural soils.Most of the estimates for the sequestrationpotential of activities listed in Table 1 range fromabout 0.3 to 0.8 t C ha1 y1, but some estimates areoutside this range (IPCC 2000a; Lal 2004a; Smithet al. 2000; Follett et al. 2000; Nabuurs et al. 1999;Smith et al. 2007a). When considering soil C seques-tration options, it is important also to consider otherside effects, including the emission of other green-house gases. Smith et al. (2001b) suggested that asmuch as one half of the climate mitigation potentialof some C sequestration options could be lost whenincreased emissions of other greenhouse gases(nitrous oxide; N2O and methane; CH4) wereincluded, and Robertson et al. (2000) has shown thatsome practices that are beneficial for SOC172 Nutr Cycl Agroecosyst (2008) 81:169178123sequestration, may not be beneficial when all green-house gases are considered. Smith et al. (2007a)showed that soil C sequestration accounts for about90% of the total global mitigation potential availablein agriculture by 2030.Other considerations for soil carbon sequestrationOne also needs to consider the trade off betweendifferent sources of carbon dioxide. For example, Nfertilizer production has an associated C cost, andsome authors have argued that the additional Csequestration for increased production is outweighedby the C cost in producing the fertilizer (Schlesinger1999). However, other studies in developing coun-tries suggest that when accounting for increasedproduction per unit of land allowed by increasedfertilizer use, and the consequent avoided use of newland for agriculture, that there is a significant Cbenefit associated with increased fertilizer use inthese countries (Vlek et al. 2004).Soil C sinks are not permanent and will continueonly for as long as appropriate management practicesare maintained. If a land-management or land-usechange is reversed, the C accumulated will be lost,usually more rapidly than it was accumulated (Smithet al. 1996). For the greatest potential of soil Csequestration to be realized, new C sinks, onceestablished, need to be preserved in perpetuity.Within the Kyoto Protocol, mechanisms have beensuggested to provide disincentives for sink reversali.e. when land is entered into the Kyoto process it hasto continue to be accounted for and any sink reversalwill result in a loss of C credits. This process istermed sink reversibility (IPCC 2000a).Soil C sinks increase most rapidly soon after a Cenhancing land-management change has beenTable 1 Examples of soilcarbon sequestrationpractices as considered bySmith et al. (2007a)Activity Practice Specific management changeCropland management Agronomy Increased productivityRotationsCatch cropsLess fallowMore legumesDeintensificationImproved cultivarsNutrient management Fertilizer placementFertilizer timingTillage/Residue management Reduced tillageZero tillageReduced residue removalReduced residue burningUpland water management IrrigationDrainageSet-aside and land use change Set asideWetlandsAgroforestry Tree crops inc. Shelterbelts etc.Grazing land management Livestock grazing intensity Livestock grazing intensityFertilization FertilizationFire management Fire managementSpecies introduction Species introductionMore legumes More legumesIncreased productivity Increased productivityOrganic soils Restoration Rewetting/AbandonmentDegraded lands Restoration RestorationNutr Cycl Agroecosyst (2008) 81:169178 173123implemented, but soil C levels may decrease initiallyif there is significant disturbance e.g. when land isafforested. Sink strength, i.e. the rate at which C isremoved from the atmosphere, in soil becomessmaller with time, as the soil C stock approaches anew equilibrium. At equilibrium, the sink has satu-rated: the C stock may have increased, but the sinkstrength has decreased to zero (Smith 2004). Thisprocess is termed sink saturation (IPCC 2000a).The time taken for sink saturation (i.e. newequilibrium) to occur is variable. The period for soilsin a temperate location to reach a new equilibriumafter a land-use change is around 100 years (Jenkin-son 1988; Smith et al. 1996) but tropical soils mayreach equilibrium more quickly. Soils in borealregions may take centuries to approach a newequilibrium. As a compromise, current IPCC goodpractice guidelines for greenhouse gas inventories usea figure of 20 years for soil C to approach a newequilibrium (IPCC 1997; Paustian et al. 1997).Meeting atmospheric CO2 concentrationstabilization targetsThe current annual emission of CO2-carbon to theatmosphere is 6.3 1.3 Pg C y1. Carbon emissiongaps by 2100 could be as high as 25 Pg C y1meaning that the C emission problem could be up tofour times greater than at present. The maximumannual global C sequestration potential is about 0.40.7 Pg C y1 (Smith et al. 2007a) meaning that evenif these rates could be maintained until 2100, soil Csequestration would contribute a maximum of about13% towards reducing the C emission gap under thehighest emission scenarios. When we also considerthe limited duration of C sequestration options inremoving C from the atmosphere, we see that Csequestration could play only a minor role in closingthe emission gap by 2100. It is clear from thesefigures that if we wish to stabilize atmospheric CO2concentrations by 2100, the increased global popula-tion and its increased energy demand can only besupported if there is a large-scale switch to non-Cemitting technologies in the energy, transport, build-ing, industry, agriculture, forestry and waste sectors(IPCC WGIII 2007).This demonstrates that soil C sequestration alonecan play only a minor role in closing the C emissiongap by 2100. Nevertheless, if atmospheric CO2 levelsare to be stabilized at reasonable concentrations by2100 (e.g. 450750 ppm), drastic reductions inemissions are required over the next 2030 years(IPCC 2000b; IPCC WGIII 2007). During this criticalperiod, all measures to reduce net C emissions to theatmosphere would play an important rolethere willbe no single solution (IPCC WGIII 2007). IPCCWGIII (2007) show that there is significant potentialfor greenhouse gas mitigation at low cost across arange of sectors, but for stabilization at low atmo-spheric CO2/GHG concentrations, strong actionneeds to be taken in the very near future, echoingthe findings of the Stern Review (Stern 2006). Giventhat C sequestration is likely to be most effective inits first 20 years of implementation, it should form acentral role in any portfolio of measures to reduceatmospheric CO2 concentrations over the next 2030 years whilst new technologies, particularly in theenergy sector, are developed and implemented (Smith2004).Overcoming barriers to implementationThere are a number of barriers that mean that theeconomic potential for C sequestration might not bereached (Smith et al. 2007a, b). These barriers mayprevent best management practices from beingimplemented. Trines et al. (2006) divided these intofive categories: economic, risk-related, political/bureaucratic, logistical and educational/societal bar-riers. Trines et al. (2006) considered barrierspreventing a range of agricultural and forestrygreenhouse gas mitigation measures (including soilC sequestration) in developed countries, developingcountries and countries with economies in transitionand Smith and Trines (2007) considered the particularbarriers prevalent in developing countries. Economic barriers include the cost of land,competing for land, continued poverty, lack ofexisting capacity, low price of C, populationgrowth, transaction costs and monitoring costs. Risk related barriers include the delay on returnsdue to slow system responses, issues of perma-nence (particularly of C sinks) and issuesconcerning leakage and natural variation in Csink strength.174 Nutr Cycl Agroecosyst (2008) 81:169178123 Political and bureaucratic barriers include theslow land planning bureaucracy and the com-plexity and lack of clarity in C/greenhouse gasaccounting rules, resulting in a lack of politicalwill. Among logistical barriers considered by Trineset al. (2006) were the fact that land owners areoften scattered and have very different interests,that large areas are unmanaged, the managedareas can be inaccessible and some areas are notbiologically suitable. The education/societal barriers relate to the sectorand legislation governing it being very new,stakeholder perceptions and the persistence oftraditional practices.Competition with other land uses is a barrier thatnecessitates a comprehensive consideration of miti-gation potential for the land-use sector. It is importantthat forestry and agricultural land managementoptions are considered within the same frameworkto optimise mitigation solutions. Costs of verificationand monitoring could be reduced by clear guidelineson how to measure, report and verify GHG emissionsfrom agriculture.Transaction costs, on the other hand, will be moredifficult to address. The process of passing the moneyand obligations back and forth between those whorealise the C sequestration and the investors or thosewho wish to acquire the C benefits, involvessubstantial transaction costs, which increases withthe number of landholders involved. Given the largenumber of small-holder farmers in many developingcountries, the transaction costs are likely to be evenhigher than in developed countries, where costs canamount to 25% of the market price (Smith et al.2007b). Organisations such as farmers collectivesmay help to reduce this significant barrier by drawingon the value of social capital. Farmers in developingcountries are in touch with each other, through localorganisations, magazines or community meetings,providing forums for these groups to set up consortiaof interested forefront players. In order for thesecollectives to work, regimes need to be in placealready, and it is essential that the credits are actuallypaid to the local owner.For a number of practices, especially thoseinvolving C sequestration, risk related barriers suchas delay on returns and potential for leakage and sinkreversal, can be significant barriers. Education,emphasising the long term nature of the sink, couldhelp to overcome this barrier, but fiscal policies(guaranteed markets, risk insurance) might also berequired.Education/societal barriers affect many practicesin many regions. There is often a societal preferencefor traditional farming practices and, where mitiga-tion measures alter traditional practice radically (notall practices do), education and extension would helpto reduce some of the barriers to implementation.But the most significant barriers to implementationof mitigation measures in developing countries (andfor some economies in transition) are economic.These are mostly driven by poverty and in some areasthese are exacerbated by a growing population. Indeveloping countries many farmers are poor andstruggle to make a living from agriculture, with foodsecurity and child malnutrition still prevalent in poorcountries (Conway and Toenniessen 1999). Given thechallenges many farmers in these regions alreadyface, climate change mitigation is a low priority. Tobegin to overcome these barriers global sharing ofinnovative technologies for efficient use of landresources and agricultural chemicals, to eliminatepoverty and malnutrition, will significantly help toremove barriers that currently prevent implementa-tion of mitigation measures in agriculture (Smithet al. 2007b). Capacity building and education in theuse of innovative technologies and best managementpractices would also serve to reduce barriers.More broadly, macro-economic policies to reducedebt and to alleviate poverty in developing countries,through encouraging sustainable economic growthand sustainable development, would serve to lower orremove barriers: farmers can only be expected toconsider climate mitigation when the threat ofpoverty and hunger are removed. Mitigation mea-sures that also improve food security and profitability(such as improved use of fertiliser) would be morefavourable than those which have no economic oragronomic benefit. Such practices are often referredto as winwin options, and strategies to implementsuch measures can be encouraged on a no regretsbasis (Smith and Powlson 2003), i.e. they provideother benefits even if the mitigation potential is notrealised.Maximizing the productivity of existing agricul-tural land and applying best management practicesNutr Cycl Agroecosyst (2008) 81:169178 175123would help to reduce greenhouse gas emissions(Smith et al. 2007b). Ideally agricultural mitigationmeasures need to be considered within a broaderframework of sustainable development. Policies toencourage sustainable development will make agri-cultural mitigation in developing countries moreachievable. Current macro-economic frameworks donot support sustainable development policies at thelocal level whilst macro-economic policies to reducedebt and to alleviate poverty in developing countries,through encouraging sustainable economic growthand sustainable development, are desperately needed.Ideally policies associated with fair trade, reducedsubsidies for agriculture in the developed world andless onerous interest rates on loans and foreign debtall need to be considered. This may provide anenvironment in which climate change mitigation inagricultural in developing countries could flourish.The UKs Stern Review (; Stern 2006) warns that unless we take actionin the next 1020 years, the environmental damagecaused by climate change later in the century couldcost between 5 and 20% of global GDP every year.The barriers to implementation of mitigation actionsin developing countries need to be overcome if weare to realise even a proportion of the 70% of globalagricultural climate mitigation potential that isavailable in these countries. Since we need to act nowto achieve low atmospheric CO2/GHG stabilisationtargets (IPCC WGIII 2007), overcoming these barri-ers in developing countries should be a priority(Smith and Trines 2007).ConclusionsLand management can profoundly affect soil C stocksand careful management can be used to sequester soilC. As with all human activities, the social dimensionneeds to be considered when implementing soil Csequestration practices. Since there will be increasingcompetition for limited land resources in the comingcentury, soil C sequestration cannot be viewed inisolation from other environmental and social needs.The IPCC WGIII (2007) have noted that global,regional and local environmental issues such asclimate change, loss of biodiversity, desertification,stratospheric ozone depletion, regional acid deposi-tion and local air quality are inextricably linked. SoilC sequestration measures clearly belong in this list.The importance of integrated approaches to sustain-able environmental management is becoming everclearer.The key to increasing soil C sequestration, as partof wider programs to enhance sustainability, is tomaximize the number of winners and minimize thenumber of losers. One possibility for improving thesocial/cultural acceptability of soil C sequestrationmeasures, would be to include compensation costs forthose who are disadvantaged when costing imple-mentation strategies. By far the best option however,is to identify measures that increase C stocks whilst atthe same time improving other aspects of theenvironment, e.g. improved soil fertility, decreasederosion, or greater profitability, e.g. improved yield ofagricultural or forestry products. There are a numberof management practices available that could beimplemented to protect and enhance existing C sinksnow, and in the future. Smith and Powlson (2003)developed these arguments for soil sustainability butthe policy options are equally applicable to soil Csequestration. Since such practices are consistentwith, and may even be encouraged by, many currentinternational agreements and conventions, their rapidadoption should be encouraged as widely as possible.Carbon sequestration measures should be consid-ered within a broader framework of sustainabledevelopment. Policies to encourage sustainable devel-opment will make soil C sequestration in developingcountries more achievable. Current macro-economicframeworks do not currently support sustainabledevelopment policies at the local level. Policies toencourage fair trade, reduced subsidies for agriculturein developed countries and less onerous interest onloans and foreign debt would encourage sustainabledevelopment, which in turn would provide an envi-ronment in which C sequestration could be consideredin developing countries (Trines et al. 2006; Smith andTrines 2007).Acknowledgements The structure of this paper is based on achapter prepared of a UN book Impact of land use change onSoil Resources (eds: AK Braimoh and PLG Vlek) but includesupdated material arising from the IPCC WGIII (2007) report andother papers and reports published during 2006 and 2007. 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Environ Dev Sust6:213233178 Nutr Cycl Agroecosyst (2008) 81:169178123Land use change and soil organic carbon dynamicsAbstractIntroductionFactors controlling the level of soil organic carbonThe role of soils in the global carbon cycleHistorical losses of SOC due to land use changeLand use change and soc lossLand use change and land management to restore or sequester socThe global potential for sequestration of SOCOther considerations for soil carbon sequestrationMeeting atmospheric CO2 concentration stabilization targetsOvercoming barriers to implementationConclusionsAcknowledgementsReferences /ColorImageDict > /JPEG2000ColorACSImageDict > /JPEG2000ColorImageDict > /AntiAliasGrayImages false /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 150 /GrayImageDepth -1 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict > /GrayImageDict > /JPEG2000GrayACSImageDict > /JPEG2000GrayImageDict > /AntiAliasMonoImages false /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 600 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict > /AllowPSXObjects false /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile (None) /PDFXOutputCondition () /PDFXRegistryName ( /PDFXTrapped /False /Description >>> setdistillerparams> setpagedevice


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