The livestock industry accounts for a considerable proportion of agricultural greenhouse gas emissions, and in response, the Australian red meat industry has committed to an aspirational target of net-zero emissions by 2030. Increasing soil carbon storage in grazing lands has been identified as one method to help achieve this, while also potentially improving production and provision of other ecosystem services. This review examined the effects of grazing management on soil carbon and factors that drive soil carbon sequestration in Australia. A systematic literature search and meta-analysis was used to compare effects of stocking intensity (stocking rate or utilisation) and stocking method (i.e, continuous, rotational or seasonal grazing systems) on soil organic carbon, pasture herbage mass, plant growth and ground cover. Impacts on below ground biomass, soil nitrogen and soil structure are also discussed. Overall, no significant impact of stocking intensity or method on soil carbon sequestration in Australia was found, although lower stocking intensity and incorporating periods of rest into grazing systems (rotational grazing) had positive effects on herbage mass and ground cover compared with higher stocking intensity or continuous grazing. Minimal impact of grazing management on pasture growth rate and below-ground biomass has been reported in Australia. However, these factors improved with grazing intensity or rotational grazing in some circumstances. While there is a lack of evidence in Australia that grazing management directly increases soil carbon, this meta-analysis indicated that grazing management practices have potential to benefit the drivers of soil carbon sequestration by increasing above and below-ground plant production, maintaining a higher residual biomass, and promoting productive perennial pasture species. Specific recommendations for future research and management are provided in the paper.

Context: Gravel fractions (>2 mm) in soil are almost always excluded from laboratory analysis and glasshouse experiments as they are considered to be inert; however, the >2 mm fraction is always present in field experiments. Aims: To determine whether the >2 mm fraction of ironstone gravel (IG) soil enriched with phosphorus (P) can supply P to wheat (Triticum aestivum L.). Methods: An IG soil was separated into different size fractions (2 mm fractions were enriched with P to different levels and added to a sand culture, or to the enriched <2 mm fraction in different amounts (25%, 50% and 75% IG). Wheat was grown in pots and growth correlated to P added from enriched soil fractions, weighted Colwell P, soil solution P concentrations and volumetric water content. Key results: The 2 mm fraction of the IG soil likely due to its greater specific surface area. Volumetric water content decreased as gravel amount increased. Wheat was more responsive to P for larger compared to smaller gravel sizes. The P-enriched IG was able to support the growth of wheat in the absence of any other P source. For the same level of P enrichment, dry matter decreased as gravel amount increased. Conclusions: The IG influences wheat growth through P retention and release and soil moisture. Volumetric water content can be reduced significantly by high gravel contents, leading to reduced wheat growth despite sufficient P fertility. Implications: Depending on the nature of the soil matrix, soils with high amounts (~50%) of larger IG are likely to require lower P applications to optimise crop yield. Soil sampling strategies and laboratory testing need to consider how to practically include the >2 mm fraction during sample collection and analysis.