History of soil science
The early concepts of soil were based on ideas developed by a German chemist, Justus von Liebig (1803–1873), and modified and refined by agricultural scientists who worked on samples of soil in laboratories, greenhouses, and on small field plots. The soils were rarely examined below the depth of normal tillage. These chemists held the ‘balance-sheet’ theory of plant nutrition. Soil was considered a more or less static storage bin for plant nutrients—the soils could be used and replaced. This concept still has value when applied within the framework of modern soil science, although a useful understanding of soils goes beyond the removal of nutrients from soil by harvested crops and their return in manure, lime, and fertilizer.
The early geologists generally accepted the balance-sheet theory of soil fertility and applied it within the framework of their own discipline. They described soil as disintegrated rock of various sorts—granite, sandstone, glacial till, and the like. They went further, however, and described how the weathering processes modified this material and how geologic processes shaped it into landforms such as glacial moraines, alluvial plains, loess plains, and marine terraces. Geologist Nathaniel Shaler (1841–1906) monograph (1891) on the origin and nature of soils summarized the late 19th century geological concept of soils.
Early soil surveys were made to help farmers locate soils responsive to different management practices and to help them decide what crops and management practices were most suitable for the particular kinds of soil on their farms. Many of the early workers were geologists because only geologists were skilled in the necessary field methods and in scientific correlation appropriate to the study of soils. They conceived soils as mainly the weathering products of geologic formations, defined by landform and lithologic composition. Most of the soil surveys published before 1910 were strongly influenced by these concepts. Those published from 1910 to 1920 gradually added greater refinements and recognized more soil features but retained fundamentally geological concepts.
The balance-sheet theory of plant nutrition dominated the laboratory and the geological concept dominated field work. Both approaches were taught in many classrooms until the late 1920s. Although broader and more generally useful concepts of soil were being developed by some soil scientists, especially Eugene W. Hilgard (1833–1916) and George Nelson Coffey (1875-1967) in the United States and soil scientists in Russia, the necessary data for formulating these broader concepts came from the field work of the soil survey.
Friedrich Albert Fallou
In his two books ‘First Principles of Soil Science’ (1857, 2nd ed. 1865) and ‘Pedology or General and Special Soil Science’ (1862) Friedrich Albert Fallou developed his collected field observations of soil into a systematic approach. He explained why soil formation was worthy of study and appealed for recognition of soil science as a discipline. In the 1862 work, he presented a proposal for soil profile description, discussed the physical and chemical properties of soils, and proposed classification of soils based on mineral properties. Vasily Dokuchaev is recognized today as more influential than Fallou, however in the years closely following Dokuchaev's death, Fallou was regarded as the founder of modern soil science by Dokuchaev’s student, influential Russian pedologist Konstantin Dmitrievich Glinka (1867-1927). Fallou’s historical status as founder is supported by Moscow soil scientist and bibliographer of Russian soil science, Arseny Yarilov, Editor of “Pochvovedenie” (meaning soil science). Yarilov titled his 1904 article about Fallou in Pochvovedenie Friedrich Albert Fallou, Founder of Soil Science.
The scientific basis of soil science as a natural science was established by the classical works of Vasily V Dokuchaev. Previously, soil had been considered a product of physicochemical transformations of rocks, a dead substrate from which plants derive nutritious mineral elements. Soil and bedrock were in fact equated. Dokuchaev considers the soil as a natural body having its own genesis and its own history of development, a body with complex and multiform processes taking place within it. The soil is considered as different from bedrock. The latter becomes soil under the influence of a series of soil-forming factors—climate, vegetation, country, relief and age. According to him, soil should be called the ‘daily’ or outward horizons of rocks regardless of the type; they are changed naturally by the common effect of water, air and various kinds of living and dead organisms.
Beginning in 1870, the Russian school of soil science under the leadership of VV Dokuchaev (1846–1903) and N. M. Sibirtsev (1860–1900) was developing a new concept of soil. The Russian workers conceived of soils as independent natural bodies, each with unique properties resulting from a unique combination of climate, living matter, parent material, relief, and time. They hypothesized that properties of each soil reflected the combined effects of the particular set of genetic factors responsible for the soil’s formation. Hans Jenny later emphasized the functionally relatedness of soil properties and soil formation. The results of this work became generally available to Americans through the publication in 1914 of K.D. Glinka’s textbook in German and especially through its translation into English by CF Marbut in 1927.
The Russian concepts were revolutionary. Properties of soils no longer were based wholly on inferences from the nature of the rocks or from climate or other environmental factors, considered singly or collectively; rather, by going directly to the soil itself, the integrated expression of all these factors could be seen in the morphology of the soils. This concept required that all properties of soils be considered collectively in terms of a completely integrated natural body. In short, it made possible a science of soil. The early enthusiasm for the new concept and for the rising new discipline of soil science led some to suggest the study of soil could proceed without regard to the older concepts derived from geology and agricultural chemistry. Certainly the reverse is true. Besides laying the foundation for a soil science with its own principles, the new concept makes the other sciences even more useful. Soil morphology provides a firm basis on which to group the results of observation, experiments, and practical experience and to develop integrated principles that predict the behavior of the soils.
Under the leadership of C. F. Marbut, the Russian concept was broadened and adapted to conditions in the United States. The concept of soil was gradually broadened and extended during the years following 1930, essentially through consolidation and balance. The major emphasis had been on the soil profile. Marbut emphasized strongly that classification of soils should be based on morphology instead of on theories of soil genesis, because theories are both ephemeral and dynamic. He perhaps overemphasized this point to offset other workers who assumed that soils had certain characteristics without examining the soils. Marbut tried to make clear that examination of the soils themselves was essential in developing a system of Soil Classification and in making usable soil maps. In spite of this, Marbut’s work reveals his personal understanding of the contributions of geology to soil science. His soil classification of 1935 depends heavily on the concept of a ‘normal soil’, the product of equilibrium on a landscape where downward erosion keeps pace with soil formation.
In 1941 Hans Jenny’s (1899–1992) Factors of Soil Formation, a system of quantitative pedology, concisely summarized and illustrated many of the basic principles of modern soil science to that date. Since 1940, time has assumed much greater significance among the factors of soil formation, and geomorphological studies have become important in determining the time that soil material at any place has been subjected to soil-forming processes. Meanwhile, advances in soil chemistry, soil physics, soil mineralogy, and soil biology, as well as in the basic sciences that underlie them, have added new tools and new dimensions to the study of soil formation. As a consequence, the formation of soil has come to be treated as the aggregate of many interrelated physical, chemical, and biological processes. These processes are subject to quantitative study in soil physics, soil chemistry, soil mineralogy, and soil biology. The focus of attention also has shifted from the study of gross attributes of the whole soil to the co-varying detail of individual parts, including grain-to-grain relationships.
In both the classification of Marbut and the 1938 classification developed by the US Department of Agriculture, the classes were described mainly in qualitative terms and not in quantitative terms that would permit consistent application of the system by different scientists. Modification of the 1938 system in 1949 corrected some of its deficiencies but also illustrated the need for a reappraisal of concepts and principles. More than 15 years of work under the leadership of Guy D Smith culminated in a new soil classification system. This became the official classification system of the US National Cooperative Soil Survey in 1965 and was published in 1975 as Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. The Smith system was adopted in the US and many other nations for their own classification system.