B A Brief History of Pedology

B.1 Introduction

Soil science is a broad field. At a foundational level, it encompasses aspects of biology, chemistry, and physics. At an earth-system level, it governs the plant’s atmosphere, ecosystems, and water cycle. And at a disciplinary level, it involves agronomists, geologists, geomorphologists, hydrologists, atmospheric scientists, and many, many others. With so much diversity, the knowledge on soil science is vast—which is fitting, as soil is “the most complex and unparsimonious of all natural science entities” (Johnson et al., 2005) and can be studied deeply for great benefit of society. Afterall, soil is everywhere humans are. However, this diversity of work, to be impactful and organized, requires a central guiding principle. It requires an answer to the question: what defines soil?

Depending on the author, there are many definitions of soil. A geomorphologist might describe soil based on the nature of weathering and disturbance of the parent material. The Soil Science Society of America defines soil as, “the unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants.” (“What is soil?”). The second edition of the NRCS’s Soil Taxonomy needs three paragraphs to define soil (Soil Survey Staff, 1999). But that is not what defines soil. The question is not how do humans define soil, rather how does nature define a soil. What natural processes or factors create soil? Identifying the processes and factors that define soil is a historied problem and the subject of an entire field, pedology.

Now, humans define pedology in a few ways, but Hans Jenny, an influential pedologist, succinctly defines pedology as the “section of the domain of soil science that studies the soil body in its natural position.” (Jenny, 1941). Further, pedology is the study of how soils form and thus provides a foundation from which soil science can grow. It explains that soil is predicable; that its formation is governed by factors and processes that can be quantified; and that climate, topography/relief, organisms, parent material, and time are the key players. This is the big idea I want to talk about—starting from the beginning, with the contributions of four revolutionary soil scientists: Friedrich Albert Fallou, Charles Darwin, Vasily Dokuchaev, and Hans Jenny.

B.2 History of Pedology

Soils have been important to human society since the beginnings of agriculture. Soils are critical to food production, and much of the field’s practical application lies therein. However, while soil science today is closely associated with agriculture, two of the earliest soil scientists came not from agronomy, but law and biology.

In 1862, Friedrich Albert Fallou, a lawyer by training, published his most well-known book titled, “Pedology or General and Special Soil Science” (Fallou, 1862). Fallou’s Pedology is the little-discussed origin of pedology. Fallou was the first to use the term pedology, suggest a new field (kingdom, in his words) of soil science, create a scientifically robust classification system, describe (although in a somewhat limited capacity) the first soil profile, and write early explanations on soil formation (Feller et al., 2022). Fallou’s ideas were novel but of limited scope, comprised of observations made within 25 km2 of his home, and minimally circulated until much later (Feller et al., 2022; Tandarich, 2002). He remains relatively unrecognized, as is true for the next soil scientist, Charles Darwin.

Charles Darwin published The Formation of Vegetable Mould through the Action of Worms: With Observations on their Habits in 1881 (vegetable mould being synonymous with soil at the time), and despite being known as Darwin’s ‘worm book,’ the book is mostly about soils (Darwin, 1881). Further, it is important to this discussion because it is one of the first and most complete explanations of the process of soil development. In his book, Darwin describes how organisms, mostly earthworms, aid in the formation of hillslopes, sort soils and create distinct textural horizons, bury large coarse fragments and ancient buildings, and contribute to the darkening of upper soil horizons. Darwin’s ideas on soil formation were early and brilliant and provide a unique, detailed mechanism for the formation of soils. However, for many reasons, Darwin’s ideas on soils would not grip the world as did his work on the theory of evolution, and in 1883, a young Vasily Dokuchaev, the future father of soil science, would publish the landmark book Russian Chernozem that would.

Different than Darwin’s worm book, Russian Chernozem provided pedology with A) broader horizons and B) applicability (Dokuchaev, 1883). Chernozem provides great detail on soils across Russia, from its most fertile breadbasket to least fertile lands. It provides evidence from years of observation that climate, parent material, and organisms are responsible for regional difference in soil fertility, and that using these factors, the landscapes can be divided into zones with predictable characteristics. Russian Chernozem was a landmark development in the field of pedology and laid the foundation for the next century of soil science—and soil science application.

As an aside, it is difficult to not compare Darwin and Dokuchaev’s contributions and impacts. Both were brilliant soil scientists with revolutionary ideas, so why is Dokuchaev the ‘father of soil science’ and Darwin the ‘worm guy’ or ‘evolution guy?’ Johnson & Schaetzl, 2015 provide a detailed analysis of the two scientists’ approaches and histories, but I instead want to highlight a nexus of society and science.

Imagine you are an American Oceanographer in the year 1966, and you have discovered an ancient structure on the bottom of the Atlantic Ocean. You publish your finding and seek funding for an expensive expedition. You are unsuccessful. Simultaneously, in 1966 the Soviet Union successfully deploys Luna 9, the first unmanned expedition to land on the moon. The competing, expensive American Apollo program has been underway for six years and is just three away from putting three astronauts on the moon. Both advancements push the limits of human knowledge, but one is more socially useful, valuable, and thus visible. The fact that Russian Chernozem was both scientifically revolutionary and practically useful propelled it to the forefront of pedology.

Many soil scientists followed Dokuchaev’s framework for soil classification and formation. However, it was in 1941 that Dokuchaev’s ideas were further established when Hans Jenny published his book Factors of Soil Formation A System of Quantitative Pedology (Jenny, 1941). Factors provides a thorough, digestible, but self-reportedly incomplete, theory for the formation of a soil based on a concise few factors. The basic theory: soil is a function of climate, organisms, relief, and parent material over time, is arguably known by every soil scientist or student of soils.

\[ s = f (cl, o, r, p, t, …) \]

Jenny provided a clear, memorable explanation for the formation of any soil based on years of observations across the United States and Europe and rigorous theory and mathematics (Jenny, 1941). The impact of Factors cannot be understated. It is the blueprint for the many editions of Soil Taxonomy (Soil Science Division Staff, 2017), which in turn has been used in creating the maps of the soils of the United States people use every day. Factors provided foundational theory to support practical decisions and was widely circulated. It is the cornerstone of pedology, and its ideas have considerable importance even today.

The theories of soil development discussed here have grown over time and today remain strong. The strongest example of this strength comes from the greatest bridge between soil science and society, agriculture, and is known as soil health or soil quality. An early adopter, Dornan and Zeiss define soil health as “the capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health” (Dornan and Zeiss, 2000). The term has been on the rise since the early 2000s in the scientific and public lenses (Fig. 2). From a pedological perceptive, soil health implies soil is a dynamic entity: one that can change over time. The word “health” implies that soil can be deemed healthy or unhealthy, and the greatest metric of soil health is organisms, the “o” of “clorpt.” The continued strength of the idea that organisms play a dominant role in changing soils is exemplified in soil health.

To conclude, soil science is ever evolving and growing. It encompasses more and more fields, scientists, and professionals every year, and none of that would be possible without the revolutionary foundations laid by scientists throughout the 19th and 20th centuries. Fallou, Darwin, Dokuchaev, Jenny, and many others contributed much to the fundamentals of soil science and should be recognized by any soil or environmental scientist. Soils drive and respond to changes in our atmospheric (cl) and land (r, o, p) systems, and we can all benefit from a shared understanding of what we call soil.

B.3 References

Asio, V. B. (2005). Comments on “Historical Development of Soil and Weathering Profile Concepts from Europe to the United States of America.” Soil Science Society of America Journal, 69(2), 571–572. https://doi.org/10.2136/sssaj2005.0571

Darwin, C. (1881). The Formation of Vegetable Mould through the Action of Worms: With Observations on their Habits (1st ed.). Cambridge University Press. https://doi.org/10.1017/CBO9780511703850

Dokuchaev, V. V. (1883). Russian Chernozem—Selected Works of V.V. Dokuchaev 1. Jerusalem (Israel) IPST.

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

Feller, C., Aeschlimann, J.-P., & Frossard, E. (2022). The contribution of Friedrich Albert Fallou to modern soil science. Journal of Plant Nutrition and Soil Science, 185(6), 766–772. https://doi.org/10.1002/jpln.202200306

Jenny, H. (1941). Factors of Soil Formation A System of Quantitative Pedology. Dover Publications. Johnson, D. L., Domier, J. E. J., & Johnson, D. N. (2005a).

Animating the biodynamics of soil thickness using process vector analysis: A dynamic denudation approach to soil formation. Geomorphology, 67(1–2), 23–46. https://doi.org/10.1016/j.geomorph.2004.08.014

Johnson, D. L., Domier, J. E. J., & Johnson, D. N. (2005b). Reflections on the Nature of Soil and Its Biomantle. Annals of the Association of American Geographers, 95(1), 11–31. https://doi.org/10.1111/j.1467-8306.2005.00448.x

Johnson, D. L., & Schaetzl, R. J. (2015). Differing views of soil and pedogenesis by two masters: Darwin and Dokuchaev. Geoderma, 237–238, 176–189. https://doi.org/10.1016/j.geoderma.2014.08.020

Soil Science Division Staff, 2017. Soil Survey Manual. United States Department of Agriculture. Agriculture Handbook 18. Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys. 2nd edition. Natural Resources Conservation Service. U.S. Department of Agriculture Handbook 436.

Tandarich, J. P., Darmody, R. G., Follmer, L. R., & Johnson, D. L. (2002). Historical Development of Soil and Weathering Profile Concepts from Europe to the United States of America. Soil Science Society of America Journal, 66(2), 335–346. https://doi.org/10.2136/sssaj2002.3350

Fallou, F. A. (1862). Pedologie oder allgemeine und besondere Bodenkunde. Schönfeld. https://www.digitale-sammlungen.de/de/ view/bsb10283420?p age=1

“What Is Soil?” Natural Resources Conservation Service, U.S. Department of Agriculture, www.nrcs.usda.gov/resources/education-and-teaching-materials/what-is-soil#:~:text=soil%20%2D%20(i)%20The%20unconsolidated,the%20growth%20of%20land%20plants. Accessed 7 Oct. 2024.