The processes that occur within soil are closely related to those in sediments and aquatic environments. They are also associated with the beginning of life on this planet. Biochemical and biological changes were associated in the earth's early stages. Molecular biomarkers, isotope modification (such as differences in 34S and 13C), and identifiable fossils are important in the study of the earth's history. The primordial soup theory of Oparin and Haldane assumed that organic compounds in water underwent polymerization and condensation reactions similar to those that describe modern soil organic matter formation. The formation of macromolecules that catalyze their own replication is known to be assisted by clays, metals, imidazole derivatives, and selective adsorption onto mineral surfaces that promote concentration and polymerization (Bada and Lazcano, 2003). Carbon and associated N substrates may have arrived on meteorites in association with minerals.
The first written history of soil and soil biota originated in the East, where scholars were recognized in the early Chinese royal courts. Coleman et al. (2004)
stated that soils were classified during the Yao Chinese dynasty from 2357 to 2261 BCE. This dynasty should be recognized for both basic and applied studies of soils as they used a soil classification for taxation purposes. The ancient Chinese regarded earthworms "as angels of the earth." Romans, such as Aristotle, considered earthworms as "intestines of the earth" (Coleman et al., 2004). Further evidence for the early recognition of soil is that the Hebrew word for soil is "adama," from which is derived Adam, the first man in Semitic religions (see Hillel, 1991). The ancient Vedic literature of India classified soils by color (and thus organic matter content) and recognized the importance of land forms, erosion, vegetation, land use, and human health implications.
Fungi were known for their fermentation reactions in wine, beer, and bread making and also as a food source that could at times be toxic. Inscriptions on Egyptian walls from 2400 BCE show the production of beer and bread involved the use of a starter and required an incubation time. Eastern, and later Roman, scholars recognized the soil-improving qualities of legumes and crop residue additions. Roman literature on agriculture and soil management was extensive. This was updated and condensed into a single volume by Petrus Crescentius in 1240 CE and for many years was copied, even into the time of the printing press (e.g., Ruralium Commodorium libri duodecin Augsburg, 1471).
Knowledge stagnated in Europe for the one and a half thousand years prior to the Renaissance at the end of the 15 th century; not from a lack of intelligence, but from the firmly held belief that the world was governed from the outside and was not an object to be questioned (i.e., intelligent design). The end of the 15th century marked the end of the Western medieval world with the emergence of the perspective that laws that govern the world are subject to study. The concept of biological and abiotic controls that can be studied and influenced by humans marked the beginning of our present knowledge of the soil biota and their processes. The ability to transmit this knowledge by the printed word after the invention of the printing press also greatly aided scientific discovery and discussion.
We are getting further away from our historical roots, an understanding of which is so important to our thinking and ability to formulate scientific questions. The advent of the computer with its easy access to recent literature seems to delay visits to the library to look at not only the original thinking in our field during the early 20th century, but also important literature from 1950 to 1980. I have tried to summarize briefly some of the important early discoveries. In doing so, I have not referred to the original literature, but to reviews often found in textbooks that should be available in many libraries. The history of our science is not merely a listing of the important discoveries, but an important example of scientific thought processes and the relation between methodology, ideas, and concepts.
Our field is still methodology-driven as shown by the great increase in knowledge being derived from molecular techniques and tracers. Another methodology breakthrough was nearly driven to excess, as shown by the fact that the three most cited papers from the Soil Biology and Biochemistry Journal from 1975 to 2000
involved the application of the fumigation technique (earlier used by Schloesing and Müntz for nitrification studies) for the measurement of microbial biomass. Today we are benefiting greatly from the availability of automated techniques, the use of computers in data transformation, modeling and knowledge dissemination, and the presence of active scientists in many new parts of the globe.
A look at our history shows how ideas were generated. It also shows that we should look at some of the misconceptions of the past to help us clearly define our thoughts and concepts. I realize that my biases show and that I have concentrated on the positive. The literature is full of examples showing that many of our founders also developed some "doozies." It would also be rewarding to look at what did not pass the test of time so that our own ideas do not end up in the same dustbin. A brief survey of citations in some search engines, such as the U.S. National Agricultural Library, Commonwealth Agricultural Bureau, ISI Science Citations, and Biological Abstracts, shows that the words "soil ecology" elicit more responses than "soil microbiology," which is followed in interest by "soil biochemistry" and "microbial ecology." There are differences in relative rankings dependent on the search engines, but processes generally involve more citations than microorganisms. Soil N is most popular, followed by soil C, N2 fixation, and the rhizosphere. The citation survey shows that new methods of analysis are being applied to continuing problems with pollutants and pesticides and their effects on the soil population. These topics are continuing to receive a great deal of attention, as is soil biodegradation. If you really want to gain a further appreciation of our field, try general search engines, such as Google, which lists 9,050,000 items for "soil microbiology," 25,100,000 for "soil ecology," and 7,800,000 for "soil biochemistry." An understanding of the interest in the word "humus" would require the perusal of 4,760,000 items. This, however, includes recipes for a common Mediterranean prepared food, hummus, so maybe a better search would be for "soil organic matter," with 14,600,000 items.
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