Long-term monitoring of soil quality changes in Northern Germany

• First detailed assessment of a German regional long-term soil monitoring network
• Loamy study sites which were converted from long-term pasture to arable land
• Significant SOC losses detected at both sites: ≈ 20% of the pre-conversion SOC stock.
• Microbiological and faunistic results underlined the impact of land-use change (LUC).
• Benchmark of the monitoring network: highly suitable to detect soil changes in time

The German regional long-term soil monitoring network (SMN) BDF-SH (Boden-Dauerbeobachtung Schleswig-Holstein) was assessed focusing on the quality of this soil monitoring network to detect and evaluate impacts of land-use change (LUC) from pasture to arable land on soil organic carbon (SOC) and biological soil properties. This included a review and evaluation of the monitoring methods to detect long-term SOC changes over time. Two loamy LUC study sites were selected from the monitoring program. The BDF-SH is not only focusing on monitoring of soil organic carbon but also on a wide range of data of soil chemistry, physics, biology and management at field scale. The quality of the SMN as a SOC monitoring was assessed using a catalogue of essential soil monitoring requirements which resulted in a classification of monitoring levels for each parameter. A SMN-specific method is given how to calculate SOC stock changes over time. Within seven and one year(s) respectively the conversion from pasture to arable land resulted in significant SOC losses of 19.4 Mg ha− 1 (19.8%) at the sandy loam site 11 and 27.2 Mg ha− 1 (20.2%) at the clay loam site 13. SOC measurements and microbiological parameters of the soil microbiological program confirmed and defined the results of the main program more precisely. Soil faunistic results underlined the impact of LUC on the soil ecosystem. Using evaluation schemes of the literature the quality of the SMN was evaluated as highly suitable to detect and evaluate SOC stock changes over time and further LUC impacts on the soil. Most of the assessed monitoring parameters of the SMN were evaluated as fulfilling the highest level. However, a SOC fractionation method could be included in the SMN to enable an even more thorough evaluation of SOC stock changes using SOC fraction measurements in process-based SOC modeling.