Cardinael Rémi1,4, Chevallier Tiphaine 1, Germon Amandine2, Jourdan Christophe3, Christian Dupraz2, Barthès Bernard G1, Bernoux Martial1, Claire Chenu4*
Quantify all organic inputs (leaf litter, fine roots, etc.) to soil Quantify and spatialize SOC stocks plot to 2 m soil depth
Identify forms of SOC stored under agroforestry
The contribution of agroforestry systems to climate change mitigation – Assessment
of C storage in soils in a Mediterranean context
1 IRD, UMR 210 Eco&Sols, Montpellier 34060, France
2 INRA, UMR 1230 System, Montpellier 34060, France
3 CIRAD, UMR Eco&Sols, Montpellier 34060, France
4 AgroParisTech, UMR Ecosys, Thiverval-Grignon 78850, France
*Corresponding author: chenu@grignon.inra.fr
Introduction
• Agroforestry systems are agroecosystems associating trees with farming practices. They provide a variety ecosystem services whilst maintaining a high agricultural production
• Trees store carbon into their biomass but also produce an important amount of fresh organic matter that could enhance soil organic carbon (SOC) stocks
• Most studies : tropical systems, upper soil layers
Objectives
Materials and methods
Results
Organic inputs SOC stocks SOC fractions
Study site
• Silty and carbonated Fluvisol
• Hybrid walnuts (Juglans regia × nigra) planted in
1995. Current density: 110 trees ha-1
• Durum wheat (Triticum turgidum) sown in the inter rows and in the agricultural control plot
Agroforestry Control
• Two pits 150 cm deep + 1 pit 400 cm deep in the agroforestry plot
• Fine root densities: mapping
• Fine root turnover: minirhizotrons at ≠ depth
• Leaf litter: four walnut trees packed with a net
• Natural vegetation in the tree rows: sampling of aboveground and
belowground biomass
• ≈ 100 soil cores sampled in both plots to 2 m soil depth
• SOC contents estimated using field visible and near infrared spectroscopy
• Bulk densities measured for each soil core
• SOC carbon stocks calculated on an equivalent soil mass basis
• Spatial distribution of SOC stocks studied using geostatistical methods
• Particle-size
fractionation at
four depths: 0-10, 10-30, 70-100 & 160-180 cm
• Organic C inputs to the soil increased by 30% in the agroforestry plot compared to the control plot
• Additional SOC storage rate was 350 ± 88 kg C ha-1 yr-1 at 0-100 cm
• ≈ 75% of additional SOC was located at 0-30 cm
• > 50% of additional SOC storage was under tree rows
• Most additional SOC was made of particulate organic matter (>50 µm)
• Total carbon (soil + tree aboveground biomass) storage rate was 1.11 ± 0.16
Mg C ha-1 yr-1
Map of cumulated SOC stocks (Mg C ha-1).
SOC stocks and organic carbon inputs in an agroforestry system.
Conclusion
• Agroforestry systems can efficiently enhance SOC stocks in
agricultural lands and contribute to climate change mitigation
Cardinael R, Mao Z, Prieto I, Stokes A, Dupraz C, Kim JH, Jourdan C, 2015. Competition with winter crops induces deeper rooting of walnut trees in a Mediterranean alley cropping agroforestry system. Plant & Soil Cardinael R, Chevallier T, Barthès BG, Saby NPA, Parent T, Dupraz C, Bernoux M, Chenu C. Impact of
agroforesty on sotcks, forms and spatial distribution of soil organic carbon. Geoderma in press
References
10 30 50 100 150 200 0 D epth (cm ) 0.19 0.11 0.06 0.36 0.52 0.33 0.39 0.13 0.42 0.74 0.46 0.73 0.32 0.15 0.17 0.49 0.33 0.28 0.20 0.27 9.9 28.3 24.3 51.4 48.7 43.2 21.5 31.5 24.5 53.4 50.5 45.1 Stocks (Mg C ha-1) Fluxes (Mg C ha-1 yr-1) Litterfall 0.44 Branches 4.5 Trunk 6.1 Herbaceous vegetation 1.6 Crop residues 0.32Tree row litter
1.37
Stump
2.3
SOC stocks Walnut trees Durum wheat Herbaceous vegetation
2.11 2.05 2.89 1.73 226.5 205.8 Sum 1 .8 − 2 .0 1 .6 − 1 .8 1 .4 − 1 .6 1 .2 − 1 .4 1 .0 − 1 .2 0 .7 − 1 .0 0 .5 − 0 .7 0 .3 − 0 .5 0 .1 − 0 .3 0 − 0 .1 0 2 4 6 8 10 12 14 16 18 20 22 24 D e p th o f th e s o il la y e r (m )
Soil organic carbon content (mg C g-1 soil)
a b b ab b a ab b a a b a a b b a ab b a a a a ab b a b c b b a Control plot Agroforestry − inter−row Agroforestry − tree row
