Increased soil organic carbon stocks under agroforestry: A survey of six diﬀerent sites in France CARDINAEL R.1,2,3*, CHEVALLIER T.1 , CAMBOU A.1,4, BÉRAL C.5, BARTHÈS B.G.1, DUPRAZ C.6, DURAND C.1, KOUAKOUA E.1, CHENU C.2 1 IRD, UMR Eco&Sols, 34060 Montpellier, France
4 AgroCampus Ouest Centre d’Angers, UPSP EPHor, 49045 Angers, France (present address)
3 CIRAD, UPR Aida, 34398 Montpellier, France (present address)
6 INRA, UMR System, 34060 Montpellier, France
2 AgroParisTech, UMR Ecosys, 78850 Thiverval-‐Grignon, France
5 Agroof, 30140 Anduze, France
IntroducFon • Agroforestry systems (AFS) associate crops and trees in the same ﬁeld • Trees store carbon into their biomass but also produce an important amount of fresh organic ma_er that could enhance soil organic carbon (SOC) stocks • Studies concerning temperate AFS are scarce and little is known concerning their impact on deep SOC stocks
• 5 silvoarable systems • 1 silvopastoral system • Adjacent agricultural plots Site
Tree density Age (trees/ha) (years) CH Luvisol 34 6
ObjecFves of the study
! Measure SOC stocks in AFS compared to agricultural plots
! QuanQfy tree aboveground C stocks
Table 1. Main site characteris%cs.
! EsQmate SOC accumulaQon rates in AFS
Fig. 1. Loca%on and descrip%on of the 6 agroforestry systems sampled in France.
Materials and methods
• Paired-‐sites (agroforestry vs agricultural control plots)
• SOC concentraQons and stocks higher in the tree rows than in the inter-‐rows and in the controls (Fig. 3)
• Three sampling pa_erns per agroforestry site (Fig. 2), ̴12 sampling point per control plot
• Total SOC stocks higher in agroforestry than in the control (Fig. 4)
• Soil cylinders sampled every 10 cm depth. Maximum sampling depth site-‐related. Measurement of bulk density and SOC concentraQons
• In the silvoarable systems, the mean SOC stock accumulaQon rate was 0.24 (0.09– 0.46) Mg C ha-‐1 yr-‐1 at a depth of 30 cm (Fig. 5).
• SOC stocks calculated on an equivalent soil mass basis • Measurement of tree aboveground biomass
Fig. 2. Sampling pa:ern.
• C accumulaQon rate was 0.65 (0.004– 1.85) Mg C ha-‐1 yr-‐1 in the tree biomass.
Fig. 4. Total organic carbon stock (Mg C ha-‐1) of the diﬀerent sites. ABG: aboveground; BLG: belowground.
Fig. 3. Soil organic carbon concentra%on (mg C g-‐1) at the diﬀerent sites.
Conclusion Agroforestry systems efficiently enhance SOC stocks in agricultural lands and contribute to climate change mitigation. These systems are also food-producing systems (compared to afforestation), and are therefore of high interest for the « 4 per 1000 Initiative »
References Cardinael R., Chevallier T., Barthès B.G., Saby N.P.A., Parent T., Dupraz C., Bernoux M., Chenu C., 2015. Impact of alley cropping agroforestry on stocks, forms and spaQal distribuQon of soil organic carbon -‐ A case study in a Mediterranean context. Geoderma 259–260, 288–299. Cardinael R., Chevallier T., Cambou A., Béral C., Barthès B.G., Dupraz C., Durand C., Kouakoua E., Chenu C., 2017. Increased soil organic carbon stocks under agroforestry: A survey of six diﬀerent sites in France. Agric. Ecosyst. Environ. 236, 243–255.
Fig. 5. SOC stock accumula%on rates as a func%on of planta%on age. Values are for the approximate top 30 cm, except for the SJ site (approximate top 20 cm, maximum soil depth).