Liebig’s research in plant biochemistry led him to recommend the use of artificial fertilizers to increase crop yields. He also studied animal biochemistry and pioneered the production of meat extract and infant formula. Although some of his ideas later proved incorrect, he advanced the understanding of biochemistry, and his chemical principles led to increased food production.
During medieval times, European agriculture slowly increased in efficiency, but the greater demands placed on the soil commonly depleted it of nutrients. The only thing that farmers generally put back into the soil was farm-animal manure. Only in the eighteenth century did an understanding of the basic chemical principles underlying plant nutrition and soil fertility begin to develop significantly. Scientific insights included a greater understanding of photosynthesis, the process by which plants convert water, carbon dioxide, and light into the organic compounds they need to survive. In 1804, Nicolas-Théodore de Saussure demonstrated that plants obtain the carbon and hydrogen they need for photosynthesis from atmospheric carbon dioxide and water, respectively. He also found that they get the rest of the nutrients they require nitrogen and mineral elements from the soil.
Over the next few decades, many researchers ignored Saussure’s findings, believing instead that plants obtain their nutrients by absorbing complex organic molecules from humus in the soil. This theory was struck down by German chemist Justus von Liebig, who, as a professor at the University of Giessen, had already pioneered research in pure chemistry and, during the late 1830’s, had turned his attention to the chemistry of life processes and to boosting food production to help feed the growing European population. In his 1840 book Die Organische Chemie in ihre Anwendung auf Agricultur und Physiologie (Organic Chemistry in Its Applications to Agriculture and Physiology, 1840), Liebig argued, more forcefully than had de Saussure, that plants obtain their nourishment from inorganic substances and that atmospheric carbon dioxide is the source of plant carbon.
Liebig recognized, as had de Saussure,
Harvesting crops removes the nutrients contained in those crops, rather than allowing them to be recycled to the soil through decomposition of the plants. As a result, the soil becomes depleted of mineral nutrients (in contrast to the supply of carbon from atmospheric carbon dioxide, which does not become exhausted). If farmers do not replenish the soil, one or more mineral nutrients will become deficient and crop yields will decrease. Liebig maintained that inorganic fertilizers are more effective than manure for restoring the soil and pioneered in advocating the use of artificial fertilizers. His book was especially influential in England, where much experimental work on Liebig’s fertilizer theories was subsequently conducted.
With regard to one of the plant nutrients, nitrogen, Liebig’s book contained an error that was to impede the reception of his overall message about fertilizers. He stated erroneously that plants obtain nitrogen, which is needed to manufacture proteins and other plant substances, from atmospheric ammonia dissolved in rainwater and absorbed by the roots. In reality, there is far too little ammonia in the atmosphere to supply the nitrogen needed by many crop plants. Like Saussure,
In 1845, using a formula devised by Liebig, the English industrial firm Muspratt and Company manufactured an artificial fertilizer that contained the important mineral nutrients potassium and phosphate, as well as a small quantity of ammonia salts. The fertilizer was a failure, partly because, to prevent it from being washed away by rain, Liebig had specified the use of insoluble forms of the minerals, which plants were unable to absorb. A few years later, the ability of soils to retain soluble mineral salts, regardless of rain, was demonstrated, and plants were shown to absorb these salts much more easily than insoluble ones.
Even after Liebig recognized his error and more soluble formulations were applied, the results were still poor because of Liebig’s failure to realize the importance of adding nitrogen to the soil. Agriculturist Sir John Bennet Lawes
Liebig was correct, however, in stressing the importance of phosphate and potassium two nutrients that, in addition to nitrogen, are the major components of modern fertilizers. His promotion of phosphate was particularly successful. Farmers had long fertilized their fields with animal bones, but Liebig suggested that bone phosphorus would be more soluble, and thus more available to plants, if it were pretreated with sulphuric acid. Lawes, in 1842, patented a process for treating phosphate rock with sulfuric acid and subsequently launched the first superphosphate factory.
There was an important additional insight in Liebig’s mineral theory: An artificial fertilizer containing a single nutrient will boost crop yield only if the soil can supply all the other nutrients that are needed. Thus, the essential nutrient that is in least supply is the controlling factor. This generalization, known as Liebig’s law of the minimum, is still a central concept in agriculture. The law has limitations, however. For example, if several nutrients are in low supply but none is very low, an increase in any of them will boost plant growth.
Liebig also studied the biochemistry of animal nutrition, respiration, and excretion and the relationship between animal and plant biochemistry. He developed a theory of animal metabolism and presented his findings in his 1842 book Die Their-Chemie: Oder Die organische Chemie in ihrer Anwendung auf Physiologie und Pathologie (Animal Chemistry: Or, Organic Chemistry in its Application to Physiology and Pathology, 1842), one of the first syntheses of animal chemistry. Although the book contained many misconceptions, it was influential and prompted further research.
Liebig’s work in animal biochemistry extended to human nutrition and food technology. He developed a concentrated beef extract. In 1866, the Liebig Extract of Meat Company was opened in Uruguay,
Although many of Liebig’s statements proved wrong, he pioneered in using a chemical approach to understanding plant and animal biology. He described the great chemical cycles in nature and led the way in applying chemistry to agriculture, food, and nutrition. His idea of the usefulness of artificial fertilizers was, in the main, correct. His book on agricultural chemistry not only helped clarify existing knowledge of plant nutrition but also marked the beginning of the systematic development of the agricultural sciences and launched a revolution in agricultural practice.
By the 1850’s, there were at least a dozen superphosphate plants in Britain and Germany, and by 1900 world production was more than 4.5 million tons a year. Superphosphate has become one of the world’s most important fertilizers. The use of fertilizers has helped support a growing population. As of the early twenty-first century, nitrogen-containing fertilizers were important in feeding about 40 percent of the world’s people. Use of fertilizers has also led to environmental problems, however. Nitrogen-laden runoff from fertilized agricultural fields pollutes surface waters. Further, production of nitrogenous fertilizers consumes large amounts of fossil fuels.
-
Brock, William H. Justus von Liebig: The Chemical Gatekeeper. Cambridge, England: Cambridge University Press, 1997. A scientific biography. -
Epstein, Emanuel, and Arnold J. Bloom. Mineral Nutrition of Plants: Principles and Perspectives. 2d ed. Sunderland, Mass.: Sinauer Associates, 2005. Describes how plants acquire and use mineral nutrients. -
Kamminga, Harmke, and Andrew Cunningham, eds. The Science and Culture of Nutrition, 1840-1940. The Wellcome Institute Series in the History of Medicine/Clio Medica 32. Atlanta: Rodopi, 1995. Includes a chapter on Liebig’s meat extract. -
Liebig, Justus von. Organic Chemistry in its Applications to Agriculture and Physiology. Translated by Lyon Playfair. London: Taylor and Walton, 1840. Liebig’s major publication on the principles of plant nutrition. -
_______. Animal Chemistry, or, Organic Chemistry in its Application to Physiology and Pathology. Translated by William Gregory. Cambridge, England: John Owen, 1842. Liebig’s major publication on his findings in animal physiology. -
Morton, A. G. History of Botanical Science: An Account of Botany from Ancient Times to the Present Day. London: Academic Press, 1981. Chapter 9 of this comprehensive volume addresses Liebig’s contributions to knowledge of plant physiology. -
Roberts, J. M. The Penguin History of Europe. London: Penguin Books, 1997. Includes discussion of the role of agricultural innovations in European history.
Saussure Publishes His Research on Plant Metabolism
McCormick Invents the Reaper
Blair Patents His First Seed Planter
Goodyear Patents Vulcanized Rubber
Pemberton Introduces Coca-Cola
Kellogg’s Corn Flakes Launch the Dry Cereal Industry
Justus von Liebig.