Key soil attributes and land-management dataset for Australian agroecosystems linking baseline and resampling surveys

The Soil Organic Carbon Monitoring project provides a dataset from 308 agricultural sites distributed across Australia's major farming regions, integrating soil attributes (biological, chemical and physical) and elemental properties with detailed temporal land-management information. Baseline soil samples were collected between 2009 and 2012 under the Soil Carbon Research Program, and the same sites were resampled between 2022 and 2025. The dataset includes laboratory measurements of soil organic carbon, total nitrogen, pH of 1:5 soil/water suspension, pH of 1:5 soil/0.01 M calcium chloride extract, electrical conductivity (EC) of 1:5 soil/water extract, whole-soil bulk density, permanganate-oxidisable carbon, and soil elemental composition measured by portable X-ray fluorescence for a wide suite of major and trace elements. Ten soil samples were collected at three depths (0 - 0.10, 0.10 - 0.20, and 0.20 - 0.30 m) on a 25 × 25 m grid, except for the rangeland sites, where a large polygon area was used as the sampling support. At some sites, cores were kept separate (not composited based on the depth supports, known as detailed sites), while at other sites, they were composited at each depth support. Particle size distribution and direct measurements of soil organic carbon fractions (particulate, humic and resistant carbon) were performed on a spatially representative subset of 300 samples, selected to capture variability in soil properties inferred through the gathered infrared spectral datasets for the whole dataset. In addition, paddock-level land-management histories spanning 2010-2023 document crop and pasture types, tillage and residue management, fertiliser application, irrigation status, and grazing. These records enable estimation of annual carbon inputs using a multi-model crop simulation ensemble. All components are spatially referenced and interoperable, allowing integration of soil properties, agriculture management practices, and positional data. This resource supports benchmarking of SOC stocks and changes, evaluation of management impacts, and development of monitoring, reporting, and verification frameworks for soil carbon and soil health in Australian agroecosystems.