Exploring the biophysical and socio-economic barriers to carbon sequestration in viticultural soils

To avoid catastrophic changes in the climate system by the end of the 21st century, the world must pursue drastic climate change mitigation strategies. All scenarios for containing the increase in global surface temperatures to below 1.5 or 2 ℃ by 2100 involve the large-scale deployment of carbon sequestration technologies. If properly managed, agricultural soils may sequester substantial amounts of atmospheric carbon dioxide in the form of soil organic carbon. However, there is a focus on arable land and grassland with regard to soil organic carbon sequestration, and research has overlooked other types of agricultural land, especially vineyards. There is a lack of evidence on the potential of vineyards to sequester carbon and participate in the global efforts to mitigate climate change via soil organic carbon sequestration. This thesis aims to quantify the carbon sink potential of vineyard agroecosystems under different soil management practices and identify the winegrowing regions where it is the highest. It also seeks to investigate the different factors that play a role in the adoption of soil organic carbon sequestration practices by winegrowers. An interdisciplinary approach was used, combining literature review, meta-analysis, machine learning and surveys to investigate the biophysical and socio-economic barriers to soil organic carbon sequestration in vineyards. A meta-analysis was performed to estimate, at the global level, the soil organic carbon sequestration rates associated with the use of different soil management practices in vineyards, based on field experiments. Results show that, under the same management practices, vineyards may sequester similar or larger amounts of organic carbon per hectare compared to other types of agricultural land. The data gathered in the meta-analysis was then used to build a model that predicts, using a random forest regression, changes in soil organic carbon stocks in vineyards under specific management practices, based on soil and climatic characteristics. The model was applied to six winegrowing countries located in Europe (Spain, France, Italy, Portugal, Germany and Austria) for a period of twenty years. The results indicate that the ability of vineyards to sequester carbon in these countries is high, though it varies greatly depending on the winegrowing regions and practices considered. To further understand the decision-making process of implementing soil organic carbon sequestration practices in vineyards, a questionnaire was circulated to winegrowers in France. It enquired about the adoption of different soil management practices, as well as vineyard attributes and winegrowers’ socio-economic characteristics, access to information, involvement in policy instruments, resources, confidence and attitudes towards soil organic carbon sequestration practices. The results from a binary logistic regression indicate that many of these factors (e.g., winegrower’s and vine’s age, farm size, certifications, use of irrigation, etc.) are involved in the adoption process of soil organic carbon sequestration practices. To complement these results, a second questionnaire was circulated to French winegrowers to investigate the motives and barriers to the adoption of soil organic carbon sequestration practices as perceived by winegrowers. Results identify the desire to achieve biophysical outcomes (e.g., returning organic matter to the soil) as a key motivation for the adoption of these practices and biophysical and technical barriers as the main barriers preventing winegrowers from adopting the practices. The findings of this thesis suggest that vineyards have an important role to play in climate change mitigation and should not be overlooked by soil organic carbon sequestration strategies, especially in countries or regions where vineyards represent an important share of the total agricultural land. However, this potential will only be realised if soil organic carbon sequestration practices are adopted by winegrowers. Further policy instruments should be developed at the local, regional, national and European levels to overcome some of the barriers currently hindering the uptake of these practices in the viticulture sector.