Carbon sequestration in Australian Vertisols under conservation agriculture – Facts and public perception

Conservation agriculture (CA) is a complex farming system that combines types of no-tillage with crop sequencing and harvest residue management. One of the main characteristics is an assumption of inevitable soil organic matter increase, which impacts carbon sequestration (CS) to mitigate climate change. This review aims to clarify the definitions of CA, and how CA Practices (CAPs) are implanted in real life farming. CS is discussed in relation to soil type, water availability, temperature, cropping duration/CAPs, and carbon and nitrogen inputs. With focus on Australian Vertisols, we show how CS is reported in research publications vs. in general communication channels which are more important for public perception, to clarify the controversy between actual effects and assumptions. The literature search included original studies and reviews from the last 30+ years as well as grey literature to shed light on public opinion. Research on Vertisols clearly showed low CS potential (max. 0.02–0.4 % SOC increase ha⁻¹ dependent on CAP type and duration) due to their high clay content (>30 %) and intrinsic organic carbon. This is amplified by climatic conditions and low crop residue. Decomposition by microorganisms may exceed the carbon input from biomass production. Therefore, CAPs mostly just slow down humus depletion. We recommend working towards a standardized nomenclature, research under the defined terms and creating incentives for farmers to switch to „real“ CA, especially in regions with high potential for CS. Furthermore, we want to raise awareness of the variability of impacts and adjust public perception accordingly.