Stockage de carbone et dynamique des matières organiques des sols en agroforesterie sous climat méditerranéen et tempéré

Agroforestry is a land use type where trees are associated with crops and/or animals within the same field. This agroecosystem could help mitigating climate change, and also contribute to its adaptation. The goal of this thesis was to evaluate the potential of soil organic carbon storage under agroforestry systems. This study was performped at the oldest experimental site in France, a trial supervised by INRA since 1995, but also at farmers' fields. Soil organic carbon stocks were compared between agroforestry and agricultural plots, down to 2 m soil depth. All organic inputs to the soil were quantified (tree roots, leaf litter, crop roots and residues). The stability of additionnal stored carbon was caracterised with soil organic matter fractionation, and soil incubations. A model of soil organic carbon dynamic was described in order to better undrestand this dynamic in agroforestry, especially in deep soil layers. This study revealed the interest and the potential of agroforestry systems in increasing soil organic carbon stocks, with accumulation rates of 0.09 to 0.46 t C ha -1 yr -1. It also reveals the role of tree rows in this storage, and the importance of carbon inputs from root mortality. However, it raises concerns about the stability of this storage.Les systèmes agroforestiers stockent du carbone dans la biomasse des arbres. Cependant leur intérêt ne se limite pas à ce carbone stocké sous forme de bois. En effet, les arbres produisent de grandes quantités de litières, et apportent également du carbone dans les horizons profonds du sol par la mortalité et l’exsudation racinaire. Or, les sols agricoles, ayant de très faibles teneurs en matière organique, ont un potentiel de stockage en carbone bien plus important que les sols forestiers. A ce jour, il n’existe pratiquement pas de travaux permettant d’avoir une estimation de l’impact des arbres agroforestiers sur le carbone du sol. La plupart des études sont en effet menées sur le stockage de carbone dans la biomasse aérienne des arbres. Une étude a ainsi estimé qu’en climat tempéré et pour des densités comprises entre 50 et 100 arbres/ha, le stockage de carbone serait compris entre 1.5 et 4 tC/ha/an, ce qui est très important comparé au potentiel de stockage d’autres systèmes de culture. On se propose donc dans ce travail de contribuer significativement à la connaissance sur les possibilités de stockage de C dans les sols en agroforesterie. Tout d’abord, nous quantifierons les stocks de C dans les parcelles agroforestières et les comparerons aux témoins agricoles. Nous étudierons également l’hétérogénéité spatiale de ces stocks, sous la ligne d’arbres ou sous la culture intercalaire, et ce à différentes profondeurs. Dans un deuxième temps, nous étudierons les entrées de carbone au sol, notamment via la mortalité racinaire des arbres. Puis, nous étudierons les processus liés à la stabilisation de ce carbone dans les horizons profonds du sol. Enfin, nous chercherons à savoir si l’apport de carbone frais dans les horizons du sol ne pourrait pas entraîner une minéralisation d’une partie du carbone stable du sol, phénomène connu sous le nom du priming effect, et qui pourrait jouer un rôle non négligeable dans le bilan de carbone de ces systèmes. La modélisation sera utilisée afin d’estimer le stockage de carbone sur le long terme. L’étude sera menée dans un contexte de système de culture méditerranéen, sur un site expérimental d’exception. L’analyse mécaniste fournira le cadre conceptuel pour la compréhension de la dynamique du C dans d’autres systèmes agroforestiers à l’avenir

Growing woody biomass for bioenergy in southern Ontario, Canada : a case study using tree-based intercropping

Paper presented at the 12th North American Agroforesty Conference, which was held June 4-9, 2011 in Athens, Georgia.In Ashton, S. F., S.W. Workman, W.G. Hubbard and D.J. Moorhead, eds. Agroforestry: A Profitable Land Use. Proceedings, 12th North American Agroforestry Conference, Athens, GA, June 4-9, 2011.During the spring of 2006, three willow varieties from SUNY-ESF (SV1, SX67 and 9882-41) were established on a marginal land in an agroforestry tree-intercropping arrangement where plots of short rotation willow were planted between rows (spaced 15 m apart) of 20-year-old mixed tree species. As a control, the same varieties were established on an adjacent piece of land without established tree rows. The study investigated the distribution of carbon and nitrogen pools, fine root biomass and clone yields in both tree-based intercropping (agroforestry) and conventional monocropping systems. Willow biomass yield was significantly higher in the agroforestry field, 4.86 and 3.02 odt ha-1 y-1 for the agroforestry and control fields, respectively. SV1 and SX67 had the highest yields and 9882-41 had the lowest. Willow fine root biomass in the top 20 cm of soil was significantly higher in the intercropping system (3000 kg ha-1) than in the conventional system (2500 kg ha-1). Differences in fine root biomass between clones followed the same order that was observed for differences in biomass yield: SV1 [greater than] SX67 [greater than] 9882-41. Leaf input was higher in the intercropping system (1900 kg ha-1) than in the monocrop system (1700 kg ha-1). Clonal differences in leaf inputs followed the same trends as those for root biomass and yield: SV1 [greater than] SX67 [greater than] 9882-41. Soil organic carbon was significantly higher in the agroforestry field (1.94 [percent]) than in the control field (1.82 [percent]). A significant difference was found between the three clones; 9882-41 had the lowest soil organic carbon of 1.80 [percent]. In December 2009, both fields were harvested (1st cycle) with Anderson bio-baler harvester. Harvesting process and bale yield data, harvest moisture content, field drying and loss of moisture etc. will also be discussed.R�mi Cardinael (1), Naresh Thevathasan (2), Andrew Gordon (2), Rachelle Clinch (3) and Idris Mohammed (2) ; 1. AgroParisTech, Paris, France. 2. School of Environmental Sciences, University of Guelph, ON, Canada. 3. Golder Associates Ltd., Mississauga, ON, Canada.Includes bibliographical references

Impact of alley cropping agroforestry on stocks, forms and spatial distribution of soil organic carbon : a case study in a Mediterranean context

UMR SYTEM : Equipe AMPLUS : Analyse et Modélisation du champ cultivé PLUrispécifiqueAgroforestry systems, i.e., agroecosystems combining trees with farming practices, are of particular interest as they combine the potential to increase biomass and soil carbon (C) storage while maintaining an agricultural production. However, most present knowledge on the impact of agroforestry systems on soil organic carbon (SOC) storage comes from tropical systems. This study was conducted in southern France, in an 18-year-old agroforestry plot, where hybrid walnuts (Juglans regia × nigra L.) are intercropped with durum wheat (Triticum turgidum L. subsp. durum), and in an adjacent agricultural control plot, where durum wheat is the sole crop. We quantified SOC stocks to 2.0 m depth and their spatial variability in relation to the distance to the trees and to the tree rows. The distribution of additional SOC storage in different soil particle-size fractions was also characterized. SOC accumulation rates between the agroforestry and the agricultural plots were 248 ± 31 kg C ha− 1 yr− 1 for an equivalent soil mass (ESM) of 4000 Mg ha− 1 (to 26–29 cm depth) and 350 ± 41 kg C ha− 1 yr− 1 for an ESM of 15,700 Mg ha− 1 (to 93–98 cm depth). SOC stocks were higher in the tree rows where herbaceous vegetation grew and where the soil was not tilled, but no effect of the distance to the trees (0 to 10 m) on SOC stocks was observed. Most of the additional SOC storage was found in coarse organic fractions (50–200 and 200–2000 μm), which may be rather labile fractions. All together our study demonstrated the potential of alley cropping agroforestry systems under Mediterranean conditions to store SOC, and questioned the stability of this storage