Management impacts on the C balance in agricultural ecosystems Jean-François Soussana 1 Martin Wattenbach 2, Pete Smith 2 1. INRA, Clermont-Ferrand, France 2. Aberdeen University, Scotland, UK CarboEurope, Poznan meeting, October 9, 2007.

Fossil fuel emissions = 1850 Mt C per year Geographic Europe Uncertainties in the carbon balance of European ecosystems before the start of CarboEurope (Janssens et al. Science, 2003). Sink Source

Components of the agricultural C budget NEE: Net Ecosystem Exchange, Atmospheric C balance NBP: Net Biome Productivity, Soil C balance

28 sites Main Grass. Main Wet. Anc. Grass. Anc. Wet. CarboEurope IP grasslands & wetlands sites

Climate drivers of grassland and wetland annual GPP at CarboEurope IP sites (n=50, r 2 =0.705, P<0.0001) Log(GPP) = Log (Temp) Log (Precip)

Mean C fluxes (gC m -2 yr -1 ) at CarboEurope grassland and wetland sites NBP = K 2 (K 1 GPP – Cut – Digest. Intake + Manure)– K 3 e LN(Q10).Tsoil/10 –F CH4-C (n=43, R 2 =0.52, P<0.001) GPP 1228 NBP 128 R auto. 615 R hetero. Litter 294 R hetero. Herbivore 46 R hetero. SOM 89 Cut 75 Intake 70 Manure 16 K 1 =0.50K 2 =0.43 K 3 = 83 Q 10 =1.21 Digest.=0.65 Enteric fermentation 3.4

Fate of NPP and manure (at C sink sites) Cut Cut & Grazed Grazed Abandoned & Wet

Current herbage utilisation is lower than maximum

Role of cutting and grazing management for NBP Maximal grazing Maximal cutting Trade-off between C sequestration and agricultural (livestock) production

Grassland GPP over Europe Data upscaling with annual means of temperature and precipitation PASIM model (Vuichard et al., 2007 GBC)

Spatial distribution of NBP of grasslands in Europe (data upscaling) Assuming a management similar to mean site management NEXT STEP: map NBP using agricultural management based on statistics

C sequestration efficiency in grasslands (data upscaling) Assuming a management similar to mean site management NEXT STEP: map NBP/GPP using agricultural management based on statistics

How large is the grassland C sink? First estimate, which needs to be refined: i)DOC/DIC losses up to 8 % of NBP ii)On site N 2 O and CH 4 emissions reach ca. 30 % of NBP iii)Indirect N2O and CH4 emissions, reach ca 15 % of NBP

CarboEurope-IP Cropland sites

(Gruenwald, pers. comm. to Christine Moureaux) Variability between years and under different crops

Using models to interpret EC data from croplands

Analysis by Mike Williams

What are the uncertainties associated with the simulation of cropland ecosystems at site level ? Input parameters and variables Uncertainty site scale Fertilization (Nitrogen) +/- 10% each application Temperature+/- 1°C Precipitation+/- 5% Global radiation+/- 5% Clay content+/- 10% Initial soil carbon+/- 10% siteNEE measured kgC ha -1 best estimate run kgC ha -1 Mean value of the Monte Carlo simulation kgC ha -1 Oensingen The discrepancy between simulated mean value from the Monte Carlo runs and the annual value obtained from a single run using the best estimates. suggest that using the best estimate may not lead to the most probable model result. Input distribution Monte Carlo – multi model run DNDC* model * DeNitrification-DeComposition model Output distribution

Are croplands as big a source of C as we thought?

Data from: Smith et al. (2007a) Looking to the future…more work on organic soils Organic soil restoration vs. mineral soil sequestration

Change in cropland SOC – climate&NPP&technology Climate only J.U. Smith et al. (2005)

Change in cropland SOC – climate&NPP&technology Climate&NPP&technology J.U. Smith et al. (2005)

Management impacts on cropland C balance – climate mitigation Smith et al. (2007a) Some potential for agricultural GHG mitigation in Europe

Conclusions Synthesis papers are being written for each landuse type Plans for whole agricultural sector. Same methodology for both land uses. Need to account better for actual agricultural management over Europe. Major challenges –Interannual variability and climate change –Continental upscaling –Organic soils –Non CO 2 GHG emissions –Interactions with mitigation and adaptation