Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/bg-2017-125
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
12 Apr 2017
Review status
This discussion paper is under review for the journal Biogeosciences (BG).
High organic inputs explain shallow and deep SOC storage in a long-term agroforestry system – Combining experimental and modeling approaches
Rémi Cardinael1,2,a, Bertrand Guenet3, Tiphaine Chevallier1, Christian Dupraz4, Thomas Cozzi2, and Claire Chenu2 1IRD, UMR Eco&Sols, Montpellier SupAgro, 2 place Viala, 34060 Montpellier, France
2AgroParisTech, UMR Ecosys, Avenue Lucien Brétignières, 78850 Thiverval-Grignon, France
3Laboratoire des Sciences du Climat et de l’Environnement, UMR CEA-CNRS-UVSQ, CE L’Orme des Merisiers, 91191 Gif-Sur-Yvette, France
4INRA, UMR System, Montpellier SupAgro, 2 place Viala, 34060 Montpellier, France
apresent address: CIRAD, UPR AIDA, Avenue d’Agropolis, 34398 Montpellier, France
Abstract. Agroforestry is an increasingly popular farming system enabling agricultural diversification and providing several ecosystem services. In agroforestry systems, soil organic carbon (SOC) stocks are generally increased, but it is difficult to disentangle the different factors responsible for this storage. Organic carbon (OC) inputs to the soil may be larger, but SOC decomposition rates may be modified owing to microclimate, physical protection, or priming effect from roots, especially at depth. We used an 18-year-old silvoarable system associating hybrid walnut trees (Juglans regia × nigra) and durum wheat (Triticum turgidum L. subsp. durum), and an adjacent agricultural control plot to quantify all OC inputs to the soil – leaf litter, tree fine root senescence, crop residues, and tree row herbaceous vegetation –, and measure SOC stocks down 2 m depth at varying distances from the trees. We then proposed a model that simulates SOC dynamics in agroforestry accounting for both the whole soil profile and the lateral spatial heterogeneity.

OC inputs to soil were increased by about 40 % (+1.11 t C ha−1 yr−1) down to 2 m depth in the agroforestry plot compared to the control, resulting in an additional SOC stock of 6.3 t C ha−1 down to 1 m depth. The model described properly the measured SOC stocks and distribution with depth. It showed that the increased inputs of fresh biomass to soil explained the observed additional SOC storage in the agroforestry plot. Moreover, modeling revealed a strong priming effect that would reduce the potential SOC storage due to higher organic inputs in the agroforestry system by 75 to 90 %. This result questions the potential of soils to store large amounts of carbon, especially at depth. Deep-rooted trees modify OC inputs to soil, a process that deserves further studies given its potential effects on SOC dynamics.


Citation: Cardinael, R., Guenet, B., Chevallier, T., Dupraz, C., Cozzi, T., and Chenu, C.: High organic inputs explain shallow and deep SOC storage in a long-term agroforestry system – Combining experimental and modeling approaches, Biogeosciences Discuss., doi:10.5194/bg-2017-125, in review, 2017.
Rémi Cardinael et al.
Rémi Cardinael et al.
Rémi Cardinael et al.

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Short summary
The introduction of trees in an agricultural field modifies organic matter (OM) inputs to the soil (litterfall, root litter...), microclimate, and stabilization and decomposition processes of OM. All these changes could affect soil organic carbon (SOC) storage but the importance of each process is not well known. In a long-term agroforestry trial, we showed that SOC storage was mainly driven by high OM inputs to the soil, but that enhanced decomposition could also have reduced this potential.
The introduction of trees in an agricultural field modifies organic matter (OM) inputs to the...
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