Soil Organic Matter as a Global Metric for Soil Health: Integrating Soil Biology and Agro-Ecosystem Management

Abstract

Soil is fundamental to sustaining life on Earth, supporting agricultural productivity, water and climate regulation and habitat for biodiversity. Increasing pressures from agricultural intensification, climate change, and land-use changes pose existential threats to our soils as well as impairing their quality or health. Both these terms are subject to considerable criticism. Consequently, accurate measurement and monitoring are essential actions to support more informed research guidelines and policies towards sustainable land management. Soil microorganisms play a crucial role in maintaining soil health by driving organic matter decomposition and nutrient cycling, soil structure formation, synthesis of bioactive compounds and promotion of plant growth. However, measuring microbial diversity and activity remains challenging because of the complexity of soil ecosystems, spatial and temporal variability, and technical limitations. While techniques like amplicon metagenomics and enzyme activity assessments provide valuable insights, their cost and operational procedures hinder large-scale application. Soil microbial activity is coupled with soil organic matter (SOM) content, which supplies the habitat, nutrients, and energy required for microbial growth. SOM and its transformations are shaped by and essential to microbial life. Predominantly related to soil microbial activity, SOM is easier to assess and can act as an indirect yet robust proxy for soil biological health and ecosystem function. Additionally, SOM also reflects important chemical and physical dimensions of soil health, serving as an operational and integrative indicator of soil quality. Advances in analytical methods, such as spectroscopic techniques and remote sensing, now allow for accurate and cost-effective quantification and monitoring of SOM. Observations made globally and over time provide a comprehensive understanding of patterns across different regions, reflecting environmental changes, different land uses and cropping systems. Access to such data helps identify emerging issues, track progress, and implement solutions that are both relevant and scalable, ensuring that policies are adaptive and impactful. We cannot afford to wait for the perfect set of indicators of soil health to address environmental and agronomic challenges. Delaying political action risks deepening the crisis and missing crucial opportunities for change. When it comes to selecting a soil health indicator, SOM is certainly the most comprehensive and one of the easiest to measure. Adopting SOM as a global metric for soil health is a practical and scientifically grounded approach. Its ability to capture key soil functions, combined with advancements in measurement technology, makes SOM a pivotal tool for safeguarding soil quality, enhancing ecosystem resilience, and ensuring long-term food security