Agricultural soils have a great potential for carbon (C) sequestration due to the build-up of soil organic matter (SOM), which consists of about 58% C. Positive efforts in SOM management could therefore make a significant contribution to climate protection. For farmers, CO2 certificates for the build-up of soil organic carbon (SOC) represent an additional incentive to implement SOM-enhancing management measures. These CO2 certificates are issued by private initiatives and companies in the voluntary CO2 market. Especially in the field of agriculture, certificate trading for sequestered C in agricultural soils is currently growing in the German-speaking countries. In order to contribute to climate protection, certain criteria must be met when issuing certificates. In practice, however, minimum scientific standards have so far been given little consideration. In this study, recommendations are given regarding the quantifcation of SOC (sampling, analytics, SOC stock calculation), an evaluation of agricultural practices for C sequestration, as well as information on general limitations regarding climate protection via CO2 certificates. Generally, CO2-certificates can give a positive impulse for farmers to deal with sustainable cultivation and SOM supply of their soils. Since SOM is a key property for many soil functions and not least soil fertility, every effort to increase SOM is important. Farmers who are interested in building up SOC should therefore receive comprehensive support and advice on site-specific and farm-specific options for the sequestration of C in their soils.

This handbook is designed to support researchers in conducting state of the art assessments for evaluating impacts of agricultural soil management. Furthermore, it is addressed to a wider audience to aid understanding and interpretation of published impact assessments results. The handbook has been produced in response to a growing awareness of the fundamental role of soils and of the importance of sustainable soil management for coping with societal challenges such as food security, climate change or biodiversity loss. The handbook is structured to follow the process of conducting impact assessments, starting with a short theoretical background, the setting of system boundaries and the definition of purpose and decision making level, and ending with methods to integrate findings for multiple impact areas into a single assessment. Readers are welcome to either follow this process and go through the handbook from start to finish, or to browse and look up individual chapters that are relevant for them. While the handbook provides a methodical guideline for structuring soil related impact assessments, it does not discuss the various indicators available to measure each impact area. This complex aspect will be addressed in detail in a separate publication. The information presented in the handbook is also available online through the BonaRes Assessment Platform (www.bonares.de/sustainability). This book is the first edition of a living document. Further editions will be published at irregular intervals to accommodate updates and new research generated within the BonaRes project.