Soil organic carbon stocks have been declining for more than a century, mostly in the tropics. Maintaining soil organic matter is critical to tackling climate change and controlling soil health. One way to address this problem is to encourage farmers to improve soil carbon on their farms. We provide an ex-ante assessment of the cost-effectiveness of innovative Agri-Environmental Measures (AEM) that subsidize the use of compost. To do so, we ran a choice experiment in Guadeloupe, in the northeastern Caribbean, where there is an urgent need to preserve soil organic matter levels. 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, as well as free technical assistance, a collective financial bonus, and the possibility of combining chemical fertilisers 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 AEM would sequester up to 25,000 teqCO2 per year at the territory level 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 reached through AEM under a variety of scenarios.

一个多世纪以来，土壤有机碳储量一直在下降，主要是在热带地区。保持土壤有机质对于应对气候变化和控制土壤健康至关重要。解决这个问题的一种方法是鼓励农民改善他们农场的土壤碳。我们对补贴堆肥使用的创新农业环境措施 (AEM) 的成本效益进行了事前评估。为此，我们在加勒比东北部的瓜德罗普岛进行了一项选择实验，那里迫切需要保持土壤有机质水平。参与的 305 名农民被要求从几个提供经济支持的 AEM 中选择一个，以换取在他们的农业活动中使用堆肥，以及免费技术援助、集体经济奖金、以及将化肥与堆肥结合使用的可能性。我们发现，提供免费技术援助使参与率提高了 30 个百分点，而提供集体奖金则使参与率提高了 14 个百分点。相比之下，包括减少化肥的要求只会使参与的可能性降低两个百分点。然后，我们估计了根据每个 AEM 提议的规定，使用堆肥将被隔离在土壤中的碳量。我们发现，最有效的 AEM 每年可在地区层面封存多达 25,000 teqCO2，而最具成本效益的计划将以每 teqCO2 约 500 欧元的成本实现这一目标。最后，