Agricultural limitations to soil carbon sequestration: Plant growth, microbial activity, and carbon stabilization.

Soil carbon (C) sequestration is an important process for mitigating climate change while improving soil productivity. At the same time, it presents challenges for nutrient availability and changing agricultural practices. The aim of this study was to survey the challenges and limitations found on pioneering farms testing C sequestration using a Finnish network of farmers testing carbon farming practices. A combination of satellite monitoring, on-site measurements and soil analysis was used to quantify and evaluate soil physical, chemical, and biological quality indicators and plant productivity on 20 farms (40 fields). The indicators were assessed through a conceptual C sequestration model, classifying them into limitations for three stages of plant growth, microbial activity or C stabilization. Based on the results, there are limitations in all three stages: plant growth is constrained by crop choices which limit leaf area and sunlight capture, microbial processing of C is limited by poor soil structure and moisture stress, and C stabilization is limited by waterlogging and sulfur deficiency. These problems were found to be widespread, but not present on all the farms. Bringing all the farms to the levels of the best performing farms could reduce the considerable gap between potential productivity and C sequestration and that achieved in practice. • Soil C sequestration can be limited by plant productivity and soil quality. • We evaluated limiting factors for 20 farms testing C sequestration practices. • Nutrient deficiencies, low plant productivity, low microbial activity and poor structure were common. • Resolving the limiting factors may improve both food production and C sequestration. [ABSTRACT FROM AUTHOR]