Ex ante assessment of the cost-effectiveness of Agri-Environmental Schemes promoting compost use to sequester carbon in soils in Guadeloupe

In this article, we provide an ex-ante assessment of the cost-effectiveness of a series of innovative Agri-EnvironmentalMeasures (AEM) that subsidize the use of compost. To do so, we ran a choice experiment in the western islands of French Polynesia where the soil organic carbon content is extremely low. The 305 farmers who participated were asked to choose one of several AEM that offer financial support in exchange for using compost in their farming activities, aswell as free technical assistance, a collective financial bonus, and the possibility of combining chemical fertilizers with composts. We found that offering free technical assistance increases the participation rate by 30 percentage points and offering a collective bonus increases it by 14 percentage points. In contrast, including a requirement on the reduction of chemical fertilization would decrease the probability of participation by only two percentage points. We then estimated the amount of carbon that would be sequestered in the soil using compost as prescribed under each of the AEM proposed. We found that the most effective AES would sequester up to 25,000 teqCO2 per ha and per year and that the most cost-effective scheme would reach this target at a cost of about 500 euros per teqCO2. Finally, we find that the so-called 4 per 1000 target could be easily reached through most cost-effective measures even if only half of the farms were enrolled in the program.