Soil organic carbon changes after 5 years of improved carbon farming practices in Finnish arable land

Increasing soil organic carbon (SOC) through climate-smart land management is considered a promising nature-based solution promoting food security and climate change mitigation, particularly in arable land due to its long history of SOC loss and its intensive management. However, the achievable potential for SOC increase, e.g., at a national scale is uncertain, with conflicting predictions resulting from empirical and modelling studies and a general lack of data from realistic experimental setups. The aim of this study was to assess the potential of improved agricultural practices to increase soil C in real, commercial farming systems in Finland and to identify possible challenges involved. The study was conducted as participatory research, with 83 volunteer farms across Finland, testing various management plans with a dedicated control and treatment plot in each farm. The tested plans included eight different practices aiming to increase photosynthesis, rooting depth, or direct exogenous C inputs to soil. The efficiency of the practices to increase C inputs was evaluated using a satellite-based method and information on crop yields and harvest provided by the farmers while SOC change was measured from soil samples in the lab. Our results show that after five years, the changes observed in SOC are marginal, mainly limited by the short duration of the study. Initial SOC content was the most important driver of SOC change while C inputs, climate and clay content were less important. Despite the short duration of this study, the established network and the implemented approach can be further used, paving the way towards precise assessment of the influence of management practices on SOC changes and soil improvement under Nordic conditions over the coming decades.