Exploring 50 years of research on soil organic carbon and its critical role in climate change mitigation through carbon sequestration in terrestrial ecosystems.
Soil is far more than just a medium for plant growth; it is the lungs of our planet and one of our most powerful weapons in the fight against climate change 2 . The organic carbon (Soil Organic Carbon - SOC) hidden within soil has the ability to absorb atmospheric carbon dioxide and stabilize the climate. Scientists have been working intensively for decades to unravel the secrets of this hidden hero.
From the first study published in 1991 to an explosion in 2020, there are now thousands of scientific articles revealing the critical role of soil in mitigating climate change 2 .
In this article, we will explore how soil organic carbon research has evolved over the past 50 years, which countries and scientists have led this field, and what methods have been developed to increase soil carbon storage capacity. This invisible world beneath our feet is guiding us in our quest for solutions to the climate crisis.
Soil is a natural carbon sink that contains more carbon than is present in the atmosphere 6 . Soil organic carbon consists of humus, plant and animal residues, and microbial biomass, and accumulates in soil through biological carbon fixation processes 5 .
Estimated organic carbon stock in the top meter of soil worldwide
Of terrestrial carbon stocks are stored in soil organic carbon
Even minor changes in soil organic carbon can significantly affect atmospheric CO₂ concentrations 5 .
Soil's carbon storage capacity makes it a natural and economical solution for combating climate change. Forests, grasslands and pastures are among the most effective carbon sinks 6 . These ecosystems absorb atmospheric carbon dioxide through photosynthesis and store carbon in the soil.
Bibliometric analysis of research on soil organic carbon reveals global trends in this field. According to one study, the vast majority of publications on the topic are in English 2 . Research is most concentrated in the soil sciences category, followed by environmental sciences, geosciences, and forestry sciences 2 .
| Category | Leading Countries/Institutions | Contribution and Impact |
|---|---|---|
| Countries | USA, China, France 2 5 | The USA leads in SOC research 2 . France has high international influence with 0.3 betweenness centrality 5 . |
| Institutions | Chinese Academy of Sciences 5 | Institution with the highest number of publications and 0.09 centrality, indicating close collaboration and significant impact 5 . |
| Scientists | Koegel-Knabner, Ingrid; Smith, Pete; Lal, Rattan 2 | Most cited authors in SOC research 2 . Kuzyakov Yakov has the highest publication record 5 . |
Soil organic carbon research has shown a shift over time from macroscopic trends to microscopic biological dynamics 5 . While initial research focused on mapping the size and general distribution of carbon stocks in soil, today researchers are trying to understand more complex processes such as how carbon is stabilized in soil, its interactions with microbial communities, and how it is protected within soil aggregates 5 .
Initial focus on quantifying carbon stocks and basic distribution patterns in different ecosystems.
Shift toward understanding carbon stabilization mechanisms and the role of soil aggregates.
Increased focus on microbial interactions, agricultural management practices, and climate change mitigation potential.
Recent research focuses on topics such as conservation tillage, carbon sequestration, microbial biomass, and driving forces (soil type, land use, environmental conditions, etc.) 5 . In particular, the impact of agricultural practices such as returning crop residues to fields, different land use changes, and vegetation restoration on soil organic carbon components has become an important focus of current research .
While global meta-analyses provide carbon accumulation rates for specific management practices, understanding how specific agricultural practices and soil properties affect soil organic carbon (SOC) accumulation within defined regions can be challenging 1 . In this context, the effect of three improved management practices—organic fertilizer application, cover crops, and no-till farming—on SOC stocks was examined at 11 different trial sites in Northwestern Europe 1 .
Duration: 5-23 years
Clay Content: 1-20%
SOC Content: 0.9-2.3%
Sampling Depth: 0-30 cm & 30-60 cm
The analyses revealed significant variation in SOC responses to management practices, even within a single climate zone 1 .
| Research Factor | Expected/Classical View | Research Finding |
|---|---|---|
| Clay Content | Primary determinant of SOC accumulation 1 | Not the primary driver of SOC accumulation 1 |
| Organic Matter Addition | Consistent SOC accumulation | Increases SOC accumulation, but effects are site-dependent 1 |
| Experiment Duration & Initial SOC | Secondary factors | The factors most strongly driving SOC accumulation 1 |
| Cover Crops & No-Till | Universal benefit | Only provided SOC accumulation when combined with frost-tolerant cover crop species and only at one site 1 |
The most striking finding of the study was that clay content was not the primary determinant of SOC accumulation. Instead, SOC accumulation was most strongly driven by the interaction between experiment duration and initial SOC stock 1 .
This finding shows how critical initial carbon levels can be for the success of applied management strategies. The research highlights the need for context-specific SOC management strategies. Instead of a "one-size-fits-all" approach, strategies that consider local realities such as a particular land's initial SOC levels and management history need to be developed 1 .
Researchers working on soil organic carbon use various advanced tools and methods to understand the complex soil system.
| Tool/Method | Function and Description |
|---|---|
| Space-Time Digital Soil Mapping (ST-DSM) | An effective method that uses soil samples collected over years and environmental covariates (climate, land cover, etc.) to create long time-series SOC maps at different depths and high resolution 7 . |
| Quantile Regression Forest (QRF) | A machine learning-based technique used to measure uncertainties in predictions made with ST-DSM 7 . |
| CiteSpace Software | Software used for bibliometric analysis that helps visualize trends, collaborations, and keyword relationships in a specific research field 5 . |
| Spectroscopic Methods | Allows rapid estimation of organic carbon content in soil samples without burning or chemical processing under laboratory conditions 2 . |
| Conservation Agriculture Practices | Includes practices such as stubble retention, cover crops, crop rotation, reduced tillage or direct seeding. Aims to reduce carbon loss and efficiently increase carbon accumulation by preserving soil structure and aggregate stability 5 . |
Creating high-resolution SOC maps across space and time
Machine learning for uncertainty measurement in SOC predictions
Bibliometric analysis and research trend visualization
Soil organic carbon research has come an extraordinary way since the 1970s. We now know that soil is not just a massive carbon reservoir, but also a dynamic system highly sensitive to our management practices. Bibliometric analyses show that research will continue to focus on carbon budgeting, food security, and public health issues 2 .
Soil is one of the most valuable and overlooked gifts we have been given in the fight against climate change. Understanding and protecting it is vital not only for agricultural productivity but also for the future of our planet.
Each new discovery by scientists about this silent world beneath the soil helps us build a more resilient and sustainable future in the face of climate change. As research continues to evolve, the critical role of soil organic carbon in global ecosystem health and climate regulation becomes increasingly clear.