Effective soil organic carbon monitoring in perennial agriculture systems - Sampling protocol development and evaluation

Perennial agriculture systems are gaining ground as a more sustainable alternative to conventional annual agriculture, partly for their potential to increase the soil organic carbon (SOC) content. Carbon farming is another hot topic for SOC sequestration, as it creates economic incentives for farmers. The main purpose of this study was to measure the baseline SOC stock for a larger research project, where the SOC balance of a field with the perennial grain Kernza™ will be compared to conventional annual crops grown on a control field during five years. The SOC stock of the test and a control plot in Alnarp, south Sweden has been determined to 136.76 Mg SOC ha-1 for Kernza™ and 150.06 Mg SOC ha-1 for the control, through extensive field sampling and laboratory analysis. When evaluating different sampling protocols regarding stratification and sample size, it was found that in order to accurately detect relevant changes in SOC over a short time frame, a large number of samples was required. In this study, stratification was not effective to reduce the required number of samples. This study implies that there is a need for robust SOC sampling designs for research and the carbon farming market alike.
Perennial agriculture is gaining traction as a more sustainable option compared to traditional annual farming methods. One reason for this shift is its potential to boost soil health by increasing soil organic carbon (SOC) content. Carbon farming, which focuses on sequestering carbon in soils as a way to mitigate climate change, is also becoming increasingly popular due to the economic incentives it offers to farmers. This MSc study aimed to develop and execute a sampling protocol for establishing a baseline for SOC levels, as part of a larger research project comparing the SOC balance of fields planted with perennial grain Kernza™ versus fields growing conventional annual crops over a five-year period. It also looked at the the efficiency of different sampling protocols for accurately detecting changes in SOC over a short timeframe, by comparing the sampling protocol developed for this study to the sampling protocol proposed by the Swedish carbon farming initiative Svensk Kolinlagring (Swedish Carbon Sequestration). This study, conducted in Alnarp, south Sweden, found that the SOC stock of the Kernza™ field was measured at 136.76 Mg SOC per hectare, while the control fields with conventional crops had 150.06 Mg SOC per hectare. This data was gathered through extensive field sampling and laboratory analysis. The difference between the two research fields was mostly due to the presence of a single outlier in the control field with unusually high SOC levels, especially at depth. Upon further investigation, it was found that the high levels at this location could possibly be explained by hydrology and land management. When comparing the different sampling protocols, it was discovered that a large number of samples were necessary to be able to accurately detect relevant levels of SOC sequestration over a short time frame. It was also found that stratification—dividing the soil into subareas with similar characteristics —did not significantly reduce the required sample s