What Does “Soil Health” Actually Mean? How Paradigm Shifts the Way We Think About Our Most Valuable Resource
This article was adapted from a review of literature conducted by Eva Wanjiru Murigi (Land Health Data Analyst, CIFOR-ICRAF)
Photo by Glen Carrie on Unsplash
The mission of the Coalition of Action 4 Soil Health (CA4SH) is to improve soil health globally.
If you’ve been following CA4SH for a while now, you’ve probably heard this before, and maybe even wondered what exactly we mean when we say “soil health.” This is a question that is approached through various schools of thought, but it is important to think about soil health, what exactly we strive to improve, and why.
As a multi-stakeholder Coalition, CA4SH approaches soil health through a holistic approach, and adopts the following definition:
“[Soil Health is] the ability of the soil to sustain the productivity, diversity, and environmental services of terrestrial ecosystems”
In this sense, soil health is an approach that encompasses socio-cultural services just as much as environmental services. It is the foundation of our food systems and a living entity. Observing soil through the lens of being more than a conglomerate of organic and inorganic materials accounts for the fact that it houses about 60% of the Earth’s species, and can contain 1 000 – 10 000 kg of microbial biomass per hectare in just the first few centimetres. In a recent article for the Journal of Soil and Water Conservation, titled Soil, soul, spirituality, and stewardship, Dr Rattan Lal concludes that “it is important to combine technical approaches with spiritual dimensions to protect, restore, and sustain soil health.” Dr Lal asserts that the environmental crisis is also a spiritual and ethical crisis, and we need an integrated approach to address the 24 billion tonnes of soil that are degraded each year through agriculture and other practices.
A brief history of “soil health”
Soil as a living entity is a progressive perspective and a relatively new one at that. Successive concepts of soil have shaped the scientific agenda since the 1980s, evolving through soil fertility to soil quality and, ultimately, to soil health.
The concept of soil fertility in the 80s aimed to optimize conditions for enhanced crop productivity by manipulating the physical and chemical properties to maximize nutrient availability. The 1990s witnessed a paradigm shift towards soil quality, acknowledging the interconnectedness of physical, chemical, and biological factors in soil ecosystems, and in the 21st century, soil health has emerged, recognizing soil as a dynamic and living entity, crucial for ecosystem services. This progression reflects a deeper understanding of the intricacies within soil ecosystems, encompassing not only agricultural productivity but also the broader well-being, biodiversity, and resilience of the soil environment.
In a recent review of contemporary literature, CIFOR-ICRAF Land Health Data Analyst, Eva Wanjiru Murigi uncovered nuances of how this affects how we value and measure soil health, and why. The exercise included a review of more than 1629 global, peer-reviewed journals from the 90s to date. This time frame aimed at capturing the foundational works that laid the groundwork for contemporary perspectives on soil health.
Research gaps and implications for practice
In the literature, Eva observed that authors across different disciplines aligned on the idea that soil health is not a static entity, but a dynamic living system influenced by various factors. However, indicators and methodologies for measuring soil health are varied and often contested, and there is little collaboration between institutions, though research is moving from the study of soil production, soil health indicators, and soil pollution to the comprehensive study of entire soil ecosystems.
Challenges in standardizing methods for assessing soil health are evident in the literature, with variations in approaches and indicators utilized by different researchers. The CA4SH Monitoring Working Group is in the final stages of preparing a set of general recommendations for monitoring soil health, and CA4SH partner the Soil Health Institute has a set of three indicators they recommend for measuring soil health. On the ground, CIFOR-ICRAF has developed the Land Degradation Surveillance Framework to assess and monitor soil and ecosystem health through a participatory sampling and monitoring design that engages farmers and land managers as associate scientists. From the review of the literature, the role of visible indicators and practicality for land managers in assessing soil health are underscored to make data and recommendations actionable for land managers.
A set of universal indicators for measuring and supporting soil health would be instrumental in driving global efforts toward scaling soil health. CA4SH is working with partners to drive this initiative and looking for opportunities to collaborate and pilot the approach.
In the meantime, being able to look to a holistic definition of soil health has been instrumental in driving advocacy for soils in the global arena. Soil is a unifier for sectors, scales, the SDGs, and more This exercise of looking back on the roots of soil health as a concept has only reinforced this.
Annotated Bibliography
In the exploration of soil quality and health, significant contributions have emerged from various studies, shedding light on the intricacies of this vital aspect of environmental sustainability.
These works collectively contribute to advancing our understanding of soil health, emphasizing the integration of physical, biological, and chemical aspects, and highlighting the importance of sustainable soil management practices for agricultural productivity and environmental health.
The following annotated bibliography provides a glimpse from Eva Wanjiru Murigi’s review of current literature on soil health.
Bünemann, E. K., Bongiorno, G., Bai, Z., Creamer, R. E., De Deyn, G., de Goede, R., Fleskens, L., Geissen, V., Kuyper, T. W., Mäder, P., Pulleman, M., Sukkel, W., van Groenigen, J. W., & Brussaard, L. (2018). Soil quality – A critical review. In Soil Biology and Biochemistry (Vol. 120, pp. 105–125). Elsevier Ltd. https://doi.org/10.1016/j.soilbio.2018.01.030
Bünemann et al. (2018) conduct a critical review of soil quality concepts, assessment methods, and indicators, with a focus on agricultural land use. The study reveals a lack of systematic evaluation of soil quality in relation to specific threats, functions, and ecosystem services. The authors advocate for interactive assessment tools that consider diverse stakeholders and address critical soil properties and processes.
Doran, J. W., & Zeiss, M. R. (2000). Soil health and sustainability: managing the biotic component of soil quality. Applied Soil Ecology, 15(1), 3–11. https://doi.org/10.1016/S0929-1393(00)00067-6
Doran & Zeiss (2000) explore the urgency of addressing declining soil health due to human activities. Published in Applied Soil Ecology, the study defines soil health as the ability of soil to function as a living system within ecosystem limits. It emphasizes the sensitivity of soil organisms to land management and climate, correlating them with beneficial soil and ecosystem functions. The study advocates for practical, comprehensible, and cost-effective indicators for land managers, identifying key aspects of soil health such as surface soil properties, soil and water nitrate levels, and organic matter levels.
Idowu, O. J., van Es, H. M., Abawi, G. S., Wolfe, D. W., Ball, J. I., Gugino, B. K., Moebius, B. N., Schindelbeck, R. R., & Bilgili, A. V. (2008). Farmer-oriented assessment of soil quality using field, laboratory, and VNIR spectroscopy methods. Plant and Soil, 307(1), 243–253. https://doi.org/10.1007/s11104-007-9521-0
Idowu et al. (2008) introduced the Cornell Soil Health Test, a comprehensive assessment tool that integrates physical, biological, and chemical indicators. This test, initiated in 2007, aids in identifying specific soil constraints and explores the potential of visible near-infrared reflectance spectroscopy for cost-effective soil health assessment. The study emphasizes the need for an inclusive strategy in soil health management beyond basic fertilizer practices.
Islam, S. M. D.-U., Bhuiyan, M. A. H., Mohinuzzaman, M., Ali, Md. H., & Moon, S. R. (2017). A Soil Health Card (SHC) for soil quality monitoring of agricultural lands in south-eastern coastal region of Bangladesh. Environmental Systems Research, 6(1). https://doi.org/10.1186/s40068-017-0092-7
Islam et al. (2017) introduce the Soil Health Card (SHC) as an alternative tool for soil quality monitoring in the coastal region of Bangladesh. The study demonstrates the effectiveness of SHC in assessing various soil parameters, aligning closely with laboratory findings. The SHC is identified as a representative, convenient, cost-effective, and easily understandable tool for marginal farmers.
Karlen, D. L., Mausbach, M. J., Doran, J. W., Cline, R. G., Harris, R. F., & Schuman, G. E. (1997). Soil Quality: A Concept, Definition, and Framework for Evaluation (A Guest Editorial). Soil Science Society of America Journal, 61(1), 4–10. https://doi.org/10.2136/sssaj1997.03615995006100010001x
The essay by Karlen et al. (1997) is a foundational work published in the Soil Science Society of America Journal. It summarizes discussions from the Soil Science Society of America's Ad Hoc Committee on Soil Quality (S-581), addressing the dynamic nature of soil quality and advocating for a holistic approach that considers the interaction of biological, chemical, and physical components. The essay emphasizes the inadequacy of measuring individual soil parameters in isolation and highlights the lack of legislative standards for soil quality, defining it as "the capacity of soil to perform its functions.”
Kibblewhite, M. G., Ritz, K., & Swift, M. J. (2008). Soil health in agricultural systems. In Philosophical Transactions of the Royal Society B: Biological Sciences (Vol. 363, Issue 1492, pp. 685–701). Royal Society. https://doi.org/10.1098/rstb.2007.2178
In their seminal work, Kibblewhite et al. (2008) emphasize the pivotal role of soil health in achieving sustainable agriculture. They identify four key functions—carbon transformations, nutrient cycles, soil structure maintenance, and pest/disease regulation—driven by a diverse range of soil organisms. The authors argue that an integrated approach, quantifying energy and carbon flow between these functions, is crucial for effective soil health assessment and management.
Lal, R. (2016). Soil health and carbon management. In Food and Energy Security (Vol. 5, Issue 4, pp. 212–222). Wiley-Blackwell Publishing Ltd. https://doi.org/10.1002/fes3.96
Lal (2016) emphasizes the pivotal role of soil organic carbon (SOC) in soil health, global food security, and environmental sustainability. The paper discusses the dynamics of SOC, the interconnected nature of soil carbon pools, and the importance of maintaining SOC levels above critical thresholds for soil structure, water retention, nutrient cycling, and gaseous emissions regulation.
Maikhuri, R. K. (2012). Soil quality and soil health: A review. In ARTICLE in INTERNATIONAL JOURNAL OF ECOLOGY AND ENVIRONMENTAL SCIENCES. http://www.researchgate.net/publication/232237296
Maikhuri (2012) provides a comprehensive review distinguishing between soil health and soil quality. They underscore the finite, non-renewable, and dynamic nature of soil as a living resource. The review emphasizes the adverse effects driven by nutrient imbalances, excessive fertilization, soil pollution, and soil loss processes, especially in developing countries. The need for a focus on soil health for sustainable agriculture and environmental health is highlighted.
Sparling, G. P., & Schipper, L. A. (2002). Soil Quality at a National Scale in New Zealand. Journal of Environmental Quality, 31(6), 1848–1857. https://doi.org/10.2134/jeq2002.1848
Sparling & Schipper (2002) address the need for soil quality information for international environmental reporting. Conducted in New Zealand, the assessment focuses on topsoil properties across various regions, soil orders, and land-use categories, emphasizing the significance of soil quality information for international reporting. The study identifies variations in topsoil properties and emphasizes seven key characteristics explaining the majority of soil property variability, contributing to soil quality awareness, land management practices, and policy development in New Zealand.
Stevens, A. W. (2018). Review: The economics of soil health. Food Policy, 80, 1–9. https://doi.org/https://doi.org/10.1016/j.foodpol.2018.08.005
Stevens (2018) highlights the significance of soil health in agricultural productivity, food quality, and environmental sustainability. The paper emphasizes the multidimensional nature of soil health beyond fertility, advocates for optimal control models in analyzing soil management economics and discusses policy implications. The integration of soil science and economics is deemed crucial for evidence-based policymaking.
Stewart, R. D., Jian, J., Gyawali, A. J., Thomason, W. E., Badgley, B. D., Reiter, M. S., & Strickland, M. S. (2018). What We Talk about When We Talk about Soil Health. Agricultural & Environmental Letters, 3(1). https://doi.org/10.2134/ael2018.06.0033
Stewart et al. (2018) address the lack of consistency in soil health measurement protocols in the United States. The meta-analysis of cover crop and no-tillage studies underscores the need for standardized soil sampling protocols and dynamic indicators like aggregate stability to advance soil health science and ensure practicality for both producers and regulators.
Winowiecki, L. (2015). Landscape-scale Assessments of Soil Health: Local Determinants of Soil Organic Carbon in Ethiopia. http://www.africover.org
The study by Winowiecki (2015) underscores the critical importance of maintaining soil organic carbon (SOC) for a healthy soil ecosystem and sustainable agricultural productivity. It highlights the recognized link between reduced SOC and land degradation, as acknowledged by the UN Convention to Combat Desertification. SOC is identified as a key indicator of soil health, influencing vital properties like cation exchange capacity and water holding capacity. Agricultural practices are noted to often lead to a decline in SOC compared to native land use, potentially contributing to land degradation, and reduced agricultural productivity.
