1 Soil andic properties as powerful factors explaining deep soil organic carbon stocks distribution: the case of a coffee agroforestry plantation on Andosols in Costa Rica Tiphaine Chevallier 1 , Kenji Fujisaki 1 , Olivier Roupsard 1,2 , Florian Guidat 3 , Rintaro Kinoshita 3,5 , Elias de Melo Viginio Filho 3 , Peter Lehner 4 , Alain Albrecht 1 5 1 Eco&Sols, IRD, CIRAD, INRA, Montpellier SupAgro, Univ Montpellier, Montpellier, France 2 CIRAD, UMR Eco&Sols, LMI IESOL, B.P. 1386 CP 18524, Dakar, Senegal 3 CATIE, Tropical Agricultural Centre for Research and Higher Education, 7170 Turrialba, Costa Rica 4 Cafetalera Aquiares S.A., PO Box 362-7150, Turrialba, 7150, Costa Rica 5 Research Center for Global Agromedicine, Obihiro University of Agriculture and Veterinary Medecine, Obihiro, Hokkaido 10 080-8555, Japan Correspondence to: Tiphaine Chevallier (tiphaine.chevallier@ird.fr) Abstract. Soil organic carbon (SOC) constitutes the largest terrestrial carbon stock. Both distribution and variation of SOC stocks are needed to constitute reference baseline for studies on temporal SOC change. Specifically, in volcanic areas, the spatial variation of soil andic properties usually explains the spatial variation of topsoil SOC contents, but SOC data for deeper 15 soil layers are needed. We measured the andic properties (e.g. pyrophosphate extractable aluminium and allophane contents) and SOC stocks down to 200-cm depth in a 1 km 2 micro-watershed covered by Arabica coffee agroforestry in Costa Rica. We used diffuse reflectance mid-infrared (MIR) spectroscopy to allow a large number of soil analysis. The objectives of our study were (i) to evaluate MIRS as a low-cost and rapid tool to measure andic properties and SOC in Andosols and (ii) to predict the level of SOC stocks down to 200-cm depth. 20 1 Introduction Soil organic carbon (SOC) is a major component of soil fertility and productivity. Being a larger pool of C than vegetation and the atmosphere combined (Lal, 2004), SOC is a potential sink for atmospheric CO2, especially where it was previously depleted by land use. Therefore, there is much research needed regarding accurate quantification and spatial pattern of SOC stocks. Many factors, including soil type, climate, topography, and vegetation biomass control the spatial variation of SOC at different 25 scales (Batjes, 2014; Jobbagy and Jackson, 2000). At the plot-scale, high spatial variation of SOC may also occur (Gessler et al., 2000) and may be affected by land use changes (Chevallier et al., 2000). These variations can increase uncertainty when comparing SOC stocks under different management practices (Costa Junior et al., 2013). Accurate approaches to apprehend SOIL Discuss., https://doi.org/10.5194/soil-2019-14 Manuscript under review for journal SOIL Discussion started: 23 April 2019 c  Author(s) 2019. CC BY 4.0 License.