How farmers approach soil carbon sequestration? Lessons learned from 105 carbon-farming plans

Highlights • 105 farmers were asked to plan for increasing carbon storage on their fields. • The plans were evaluated through expert panel and simplified carbon balance modeling. • Farmers chose methods with co-benefits to soil productivity and yield. • Most plans were suitable for research and show potential for C-sequestration.Soil carbon sequestration is a recognized climate mitigation method, but it involves changes in the practices of more than 0.5 billion farms worldwide. Regionally customized carbon-farming programs are one way to tailor soil carbon storage to local conditions. We conducted farmer participatory research on 105 Finnish farms to investigate how farmers approach carbon (C) sequestration. We conducted training for farmers in the basics of carbon-farming and instructed them to make a Carbon Farming Plan for one of their fields. The plans were evaluated by a team of experts and through soil C balance calculations. In addition, potential nutrient limitations and the existing C stock were identified from soil tests. Although the existing C stocks were relatively high, an assessment of the plans indicated high potential for additional C storage (median 320 kg C ha−1year−1). The plans did not show any sensitivity to the existing C stock, with similar C inputs planned for low organic matter (OM) and high OM soils. The farmers either did not know their C stock or were not familiar with the C balance concept. Most soil samples showed considerable nutrient deficiencies (P, S, B and Mn), which can limit C storage. The quality of most plans was adequate for research with minor modifications. The largest C storage potential was estimated for measures with large additions of nutrient-poor amendments or in grazing. Most farmers chose measures with relatively low C storage benefits but high potential benefits for soil structure and productivity (cover crops, nutrient-rich amendments, grassland management). The C gain from some measures (subsoiling, diversity in grasslands) could not be estimated with current methodologies. The magnitude of planned C storage over 5 years on most farms was so small (