Mapping and comparing the distribution of soil carbon under cropping and grazing management practices in Narrabri, north-west New South Wales

The reliable assessment of soil carbon stock is of key importance for soil conservation and mitigation strategies related to reducing atmospheric carbon. Measuring and monitoring soil carbon is complex because carbon pools cycle and rates of carbon sequestration vary across the landscape due to climate, soil type, and management practices. A new methodology has been developed and applied to make an assessment of the distribution of total, organic, and inorganic carbon at a grains research and grazing property in northern New South Wales at a high spatial resolution. In this study, baseline soil carbon maps were created using fine resolution, geo-referenced, proximal sensor data. Coupled with a digital elevation model and secondary terrain attributes, all of the data layers were combined by k-means clustering to develop a stratified random soil sampling scheme for the survey area. Soil samples taken at 0.15-m increments to a depth of 1m were scanned with a mid-infrared spectrometer, which was calibrated using a proportion of the samples that were analysed in a laboratory for total carbon and inorganic carbon content. This combination of new methodologies and technologies has the potential to provide large volumes of reliable, fine resolution and timely data required to make baseline assessments, mapping, monitoring, and verification possible. This method has the potential to make soil carbon management and trading at the farm-scale possible by quantifying the carbon stock to a depth of 1m and at a high spatial resolution.