Total nitrogen levels as a key constraint on soil organic carbon stocks across Australian agricultural soils.
Journal:
Environmental research
Published Date:
May 9, 2025
Abstract
Understanding how pedoclimatic drivers regulate soil organic carbon (SOC) stock is crucial for gaining insights into terrestrial carbon-climate feedback and thus adaptation to climate change. However, current data-driven SOC predictive models often neglect to incorporate total nitrogen (TN) data, thereby constraining our understanding of carbon-nitrogen interactions and their influence on SOC storage mechanisms across large scales. Utilizing an interpretable machine learning technique, we investigate how key drivers (TN, climate, elevation, land use, pH, SiO) affect SOC stocks at different soil depths across Australian major agricultural production regions. Incorporating TN into data-based SOC predictive models enhanced the explained variation by approximately 11%. TN was identified as the predominant factor influencing SOC stocks, accounting for over 47% of observed variability across all depths and outweighing climate effects in subsurface soils. Furthermore, we identified depth-specific thresholds of TN levels that constrain SOC accumulation: 1.45 mg/g soil for 0∼10 cm, 0.80 mg/g soil for 10∼20 cm and 0.63 mg/g soil for 20∼30 cm. Projections of SOC stocks under different scenarios suggest that achieving these TN thresholds can promote SOC accumulation and help offset SOC losses associated with a 1°C increase in mean annual temperature. This study underscores TN levels as a key constraint on SOC stocks across Australian agricultural soils, and thus should be explicitly considered when predicting large-sale SOC dynamics and formulating soil carbon sequestration strategies.
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