Environmental impacts of dairy farming intensification and land use on soil organic carbon stocks and physicochemical properties

The intensification of livestock farming systems can pose significant environmental challenges, including impacts on soil physicochemical properties, carbon sequestration, and biodiversity. This study is the first to quantify the combined effects of dairy system intensification and land-use allocation on soil organic carbon (SOC) stocks and physicochemical properties at the commercial farm scale. We compared confinement and pasture-based systems across five land-use types: improved pasture (IP), mixed pasture-cropping (MPC), cropping, tree areas (TA), and natural pasture (NP, exclusive to pasture-based systems). A total of 810 soil samples were collected from the top 30 cm across nine farms in New South Wales, Australia. Pasture-based farms stored 75% more SOC and 65% more total nitrogen (TN) per hectare than confinement farms, although differences were partly influenced by regional climate and parent material. Interactions between farming system and land use showed that SOC and TN stocks were highest in IP and TA within pasture-based systems. Conversely, total phosphorus (TP) stocks were 3.7 times higher in confinement systems, independent of SOC patterns. Within pasture-based farms, NP consistently had the highest SOC and TN stocks. These results highlight that dairy system intensification interacts with land-use and environmental conditions to shape soil organic carbon and nutrient stocks. The findings provide policy-relevant benchmarks for soil‑carbon accounting and emphasize the need for regionally adapted land-management strategies and future work quantifying annual SOC sequestration rates under commercial dairy conditions. • First farm-scale assessment of dairy intensification effects on soil properties. • Pasture-based systems store more soil carbon and total N than confinement farms. • Tree areas and natural pastures act as strong soil carbon hotspots. • Soil carbon land-use differences lessen in low-rainfall confinement regions. • Findings support better policy and soil‑carbon accounting for dairy systems.