Modelling Soil Organic Carbon Dynamics at the Continental Extent Using Pedogenon Mapping

Abstract

Soil organic carbon (SOC) plays a critical role in key soil functions, yet SOC is highly vulnerable to human activities, which can shift soil from acting as a net carbon sink to becoming a net carbon source. Despite considerable efforts to monitor soil conditions, traditional evaluations often focus on temporal comparisons within similar locations, which can limit the understanding of broader changes. To address these challenges, this study employs the pedogenon map framework to systematically compare SOC changes in soils under natural conditions (genosoils) and those affected by human activity (phenosoils) across Australia. By analysing SOC fractions with different mean residence times – mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) – the study aims to assess the durability of SOC changes over time. The methodology includes selecting soil profiles within pedogenons, evaluating SOC changes, and estimating the impact of these changes on SOC's residence time using the soil tonne-year carbon (STYC) metric. The findings reveal significant spatial variations in SOC changes and their impact on residence time. Areas where SOC increased are mainly due to genosoils with lower SOC values, while genosoils with high SOC values have significantly decreased when converted to phenosoils, reflecting potentially unsustainable agricultural practices. Similar results have been found concerning the residence time of SOC regarding the genosoils SOC values. The study demonstrates that the pedogenon map is an effective tool for detecting SOC changes due to human activities, providing a robust framework for assessing soil carbon storage and informing targeted remediation strategies.