Agroforestry for a climate-smart agriculture – a case study in France. [P95]

Agroforestry is a land use type where crops and trees are grown together in the same place and at the same time. Agroforestry systems have the advantage of providing multiple products (e.g. wood, fruits) or services (e.g. biodiversity enhancement, erosion control) whilst maintaining agricultural production. If they are known to store carbon into the biomass of the trees, they could also increase soil organic carbon (SOC) stocks. However their impact has rarely been studied under temperate conditions and has mostly concerned superficial soil layers. Our objectives were (i) to quantify and spatialize SOC stocks in an agroforestry system and in an adjacent agricultural plot, (ii) to assess what SOC fractions are responsible for possible additional carbon storage, and (iii) to quantify all organic inputs entering the soil. The trial was established in 1995 in southern France. Hybrid walnut trees are intercropped with durum wheat. SOC stocks were measured on 200 soil cores down to 2 m soil depth, and particle-size fractionation was performed on 64 soil samples. Carbon stocks of trees and of the herbaceous vegetation in the tree rows were also quantified. A trench was dug to 4 m soil depth to quantify tree fine root distribution and biomass. Minirhizotrons were installed at different depths to study tree fine root turnover. Annual additional SOC storage rates were estimated at 259 ± 59 kg C ha-1 yr-1 (0-30 cm) and at 350 ± 88 kg C ha-1 yr-1 (0-100 cm), and were mainly due to particulate organic matter fractions (> 50 μm). Only 10 to 15% was associated to clay particles. When the biomass of the trees was taken into account, total organic carbon storage rate reached 1.2 Mg C ha-1 yr-1. High tree root densities were observed at depth, but root turnover decreased with depth. Agroforestry systems provide higher amounts of carbon at depth than other agricultural practices, like no-till farming, and could therefore provide a more stable C storage in the long-term. (Résumé d'auteur

The contribution of agroforestry systems to climate change mitigation – Assessment of C storage in soils in a Mediterranean context. [P-2218-01]

Agroforestry is a land use type where crops and trees are grown together in the same place and at the same time. Agroforestry systems have the advantage of providing multiple products (e.g. wood, fruits) or services (e.g. biodiversity enhancement, erosion control) whilst maintaining agricultural production. If they are known to store carbon into the biomass of the trees, they could also increase soil organic carbon (SOC) stocks. However their impact has rarely been studied under temperate or Mediterranean conditions and has mostly concerned superficial soil layers. Our objectives were (i) to quantify and spatialize SOC stocks in an agroforestry system and in an adjacent agricultural plot, (ii) to assess what SOC fractions are responsible for possible additional carbon storage, and (iii) to quantify all organic inputs entering the soil. The trial was established in 1995 in southern France. Hybrid walnut trees are intercropped with durum wheat. SOC stocks were measured on 200 soil cores down to 2 m soil depth, and particle-size fractionation was performed on 64 soil samples. Carbon stocks of trees and of the herbaceous vegetation in the tree rows were also quantified. A trench was dug to 4 m soil depth to quantify tree fine root distribution and biomass. Minirhizotrons were installed at different depths to study tree fine root turnover. Annual additional SOC storage rates were estimated at 259 ± 59 kg C ha-1 yr-1 (0-30 cm) and at 350 ± 88 kg C ha-1 yr-1 (0-100 cm). Additional storage was mainly due to particulate organic matter fractions (> 50 μm) and 10 to 15% was associated to clay particles. When the aboveground biomass of the trees was taken into account, total organic carbon storage rate reached 1.11 ± 0.16 Mg C ha-1 yr-1. High tree root densities were observed at depth, but root turnover decreased with depth. Agroforestry systems provide higher amounts of carbon at depth than other agricultural practices, such as no-till farming, and could therefore provide a more stable C storage in the long-term. (Résumé d'auteur

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

A global meta-analysis of soil organic carbon in the Anthropocene

Anthropogenic activities profoundly impact soil organic carbon (SOC), affecting its contribution to ecosystem services such as climate regulation. Here, we conducted a thorough review of the impacts of land-use change, land management, and climate change on SOC. Using second-order metaanalysis, we synthesized findings from 230 first-order meta-analyses comprising over 25,000 primary studies.We show that (i) land conversion for crop production leads to high SOC loss, that can be partially restored through land management practices, particularly by introducing trees and incorporating exogenous carbon in the form of biochar or organic amendments, (ii) land management practices that are implemented in forests generally result in depletion of SOC, and (iii) indirect effects of climate change, such as through wildfires, have a greater impact on SOC than direct climate change effects (e.g., from rising temperatures). The findings of our study provide strong evidence to assist decision-makers in safeguarding SOC stocks and promoting landmanagement practices for SOC restoration. Furthermore, they serve as a crucial research roadmap, identifying areas that require attention to fill the knowledge gaps concerning the factors driving changes in SOC

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

Soil organic carbon storage, nitrous oxide emission and net climate benefit of conservation agriculture: Insights from two long-term experiments in Zimbabwe

The slow increase in grain production in sub-Saharan Africa (SSA) is largely the result of cropland expansion rather than an increase in crop yields, which have been stagnantly low (< 1.5 t ha-1). Sustainable intensification of crop production is therefore needed to feed a growing population whilst minimizing negative impacts on the environment, biodiversity, and climate. Full accounting of the net global warming potential (GWP) of management practices can provide a holistic approach for identifying cropping systems that promote sustainable agriculture intensification to ensure food security whilst mitigating climate change