Balkovič, J.

van der Velde, M.

International Institute for Applied Systems Analysis (IIASA)

Crop residue management to save organic carbon in European agricultural soilsAgricultural land has a high potential for carbon sequestration and quantification of emissionsversus burial of C is a high priority (Lal, 2004). Shifting from conventional to carbon-friendly landcultivation preferring reduced or minimum tillage systems was suggested as a measure todecrease GHG emissions and promote SOC sequestration. Large-scale implementations ofbiophysical models are increasingly used to quantify impacts of crop management strategies inagricultural sector (e.g., van der Velde et al. 2009).In this study we use an European implementation of the Environmental Policy IntegratedClimate model (EPIC, Williams 1995) with the use of coarse resolution data that are available atEuropean scale to evaluate impacts of reduced opposed to conventional tillage on the SOC stocksunder a winter wheat production system. The two tillage systems imply different crop residuemanagement (CRM) as they differ in their effectiveness in mixing crop residues into soil. We focuson changes in topsoil SOC stocks and soil erosion.Juraj Balkovič & Marijn van der VeldeEcosystems Services and Management Program (ESM), International Institute for Applied Systems Analysis (IIASA), Laxenburg, AustriaE-mail: balkovic@iiasa.ac.at, velde@iiasa.ac.atIntroductionEuropean EPIC implementationAcknowledgement: The research leading to these results has received funding from the European Community’s Seventh Framework Programme(FP7/2007-2013) under grant agreement Nr. 226701 (CARBO-Extreme)Validation against EUROSTAT yieldsSOC changesWinter wheat production system setup comprises spatially explicit a) sowing densities, b)Potential Heat Units (PHU), c) sowing and harvesting dates, and d) maximum annualapplication of N,P,K fertilizers. Wheat was simulated in 1-year mono-crop rotation on all cropland.Fig. 1. Schematic diagram of the European EPICimplementation. S – soil and topographical database, M –meteorological database, O/C – field operation scheduleand EPIC control database, R – results databaseData sources:− JRC’s MARS meteorological data 1995-2007− CORINE 2000 and PELCOM− SRTM and GTOPO− European Soil Bureau Database, v.2− Geographic Information System of the EC− European River Catchment Database, v. 2− Statistical Office of the European CommunitiesIntegration with GIS and Up-Scaling:− Loose coupling of EPIC v. 0810 with ArcGIS− Constructed over the INSPIRE-compliant 1km grid− 1st-level integration through HomogeneousResponse Units (HRU): a unique combination ofelevation, slope, soil texture, soil depth andstoniness classes− 2nd-level Integration through Simulation Units(SimU): a unique combination of HRU, NUTS2,land cover, and watershed; 38 738 SimUs forarable landConventional versus reduced tillageWe evaluate a shifting from conventional to reduced tillage systems. The two tillage systemsdiffer in their effectiveness in mixing crop residues into soil. The other crop management options(e.g. fertilization) remained constant.Since crop growth determines the accumulation of biomass, it represents a precondition for SOCsequestration. The EPIC model was therefore validated for the simulated yields to match theobserved yields reported by EUROSTAT. A comparison between simulated and observed annualyields aggregated at NUTS2 level is presented in Fig. 2a. EPIC slightly under-predicted yields inhighly productive regions of Western Europe. The systematic error in the EPIC simulations ispresented through relative errors in Fig. 2c.Fig. 2. (a) scatter plot with means and +/- SD of simulated versus observed regional yields (average of 1997-2007), (b) simulatedWWHT yields in t ha–1, (c) relative estimation error in %a. b. c.Conventional tillage• Mouldboard plough• Tillage depth: 150mm• Mixing efficiency: 99%• Crop residue left on soil: 1%Reduced tillage• Disk and chisel plough• Tillage depth: 150mm• Mixing efficiency: 85%• Crop residue left on soil: 15%Fig. 3. Average annual change in the total topsoilSOC (OCPD) when converting from conventional toreduced tillage (dashed line denotes the EUaverage).The reduced tillage management increased thetopsoil SOC stock (OCPD) by about 4% (+1.7t/ha) on average for whole of Europe (the Pvalue for the paired t-test < 0.001) compared tothe conventional tillage. The average annualincrease was about 1% (328 kg/ha), 0.5% (86kg/ha), 22.6% (340 kg/ha) and 24.7% (930 kg/ha)for SOC in passive humus, slow humus,metabolic litter and structural litter, respectively.The labile SOC pools were affected more thanthe slow and passive SOC. However, thesimulated SOC changes vary by regions (Fig. 3)depending on different climatic, site and nutrient-input conditions.Fig. 4. Impact of mean annual temperature andprecipitation on (a, b) OCPD change and (c, d) theOCPD change relative to 1 t/ha yield whenconverted from conventional to reduced tillageSoil erosiona bc dTemperature (T) and precipitation (PREC) aremajor climatic drivers affecting the SOCdynamics. Higher PREC together with moderateT promote SOC accumulation in conservationCRM (Fig. 4 a-b). It is because these conditionsincrease the accumulation of wheat biomass andthus crop residue inputs. Since OCPD, andespecially its structural litter component, areintensively transformed into CO2 or moreresistant SOC under these conditions, EPICexpects a decrease in ∆OCPD with increasingPREC when evaluated relative to a unit wheatyield (Fig. 4c), indicating that the net increase in∆OCPD relative to PREC in Fig 4b. is caused byan increase in crop biomass.Fig. 6. Probability of an extreme erosion event(MUSLE, conventional tillage)Fig. 7. Average annual change in the annual SOC loss withsediments when converting from conventional to reduced tillageSoil erosion causes a substantial loss of soilmaterial on European cropland as indicated by theMUSLE method in EPIC. The distribution ofannual soil erosion under conventional winterwheat production system is presented in Fig. 5. Inaddition, the EPIC simulations enable identifyinghot-spots with a high probability of extremeerosion events (Fig. 6). Reduced tillage cansignificantly decrease the SOC losses with soilsediments (YOC) compared to conventional tillage(Fig. 7).ConclusionsConservation tillage practices may enhance SOC sequestration and help to control SOC losses withsediments. Fig. 8 demonstrates the SOC stock gained from the reduced tillage relative to theconventional tillage for the winter wheat productionsystem. Reduced tillage was identified as aneffective measure to control both erosion andSOC stocks in agricultural soils.The European EPIC implementation is a usefultool to asses environmental impacts ofalternative crop management strategies in theagricultural sector.Fig. 5. Average annual soil loss by water erosionunder a wheat production system (MUSLE,conventional tillage)Fig. 8. Average annual change in OCPD in agricultural soilsunder winter wheat production system when converting fromconventioanl to reduced tillage.ReferencesLal, R. 2004. Soil carbon sequestration Impacts on global climate change and food security. Science 304, 1623-1627.van der Velde, M., Aloe, A., Bouraoui, F. 2009. Pan-European regional-scale modelling of water and N efficiencies of rapeseed cultivation for biodieselproduction. Glob. Change Biol. 15, 24-37.Williams, J.R., 1995. The EPIC model. In: Singh, V.P. (ed.), Computer models of watershed hydrology, pp. 909-1000, Water resources publisher, Colorado,USA.

Crop residue management to save organic carbon in European agricultural soils

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