The German Genius

Liebig laughed at the folly of it all, yet when it opened in 1868, it was immediately swamped by the demand. 21
    T HE A GE OF F ERTILIZERS
     
    Von Liebig, as we have noted, was a combustible character. It should, therefore, not be too much of a surprise to learn that, around 1840, he underwent a sudden scientific change of life and abandoned the theoretical aspects of organic chemistry for the much more practical interests of agriculture. 22 The change was, nonetheless, provoked by his interest in carbon. In an analysis of strawberries and fruits, he had found that, in a given area of land, whether it was cultivated fields or “wild forest,” the same total quantity of carbon was produced each year in the composition of whatever plants grew in it. This was the starting point for what became a bitter argument as to whether such carbon derived from the atmosphere or from the humus in the soil. The dispute arose because von Liebig had long been interested in the source of nitrogen. He had found ammonia in the body of every plant he investigated and this persuaded him that it must come from ammonia dissolved in rainwater, which, he found, always contained certain amounts of that substance. The more he looked at plants, the more uniformities he found. Such uniformities, von Liebig thought, could not be accidental, and he concluded, controversially, that the nutrients in the soil and air were inorganic not organic. 23
    He put this together into what has been called “the most comprehensive picture of the problem of plant nutrition that had ever been presented.” Von Liebig’s Organic Chemistry in Its Applications to Agriculture and Physiology , London, 1840, beginning with the role of carbon in plant nutrition, refuted the then widely held view that humus—decayed plant matter—formed the main nutrient substance for plants. Von Liebig’s second argument was that the source of carbon assimilated into plants is the atmosphere. The function of plants, he argued, was to separate the carbon and oxygen of carbonic acid, “releasing the oxygen and assimilating the carbon into compounds such as sugar, starch and gum.” 24
    This argument for a chemical understanding of the internal processes of vegetables (further evidence to discredit the “vital force”) was, however, not what made von Liebig’s book the sensation it was. What drew attention was his view that certain nutrient materials—external sources—were essential for plant growth, for these were conclusions that impinged directly on agricultural practices. For von Liebig, the very idea of fertilizer meant adding to the soil what nutritional elements were not supplied naturally from the atmosphere. Fertilizers, he said, should comprise not humus but bases such as lime, potash, and magnesia, plus phosphoric acid, the best source of which was pulverized animal bones.
    Von Liebig’s book provoked intense interest among agriculturalists, particularly in Britain and America. At Rothamsted experimental farm in England, von Liebig’s fertilizers were tested on wheat and found to have no noticeable effect on production, whereas ammonium salts added to the soil brought about great improvements in the harvests year after year. These results blew a hole in von Liebig’s entire “mineral theory,” or so it was thought, and his ideas were dismissed. Von Liebig didn’t give way, however, though it would be another decade before he solved the problem. He had been too worried that soluble salts would be leached away by rainwater—in fact, the topsoil absorbed them. And, despite the early doubts, von Liebig’s book changed completely attitudes to scientific agriculture. Before 1840, the conventional wisdom was that both plants and animals needed organic—previously living—material in order to survive. Following von Liebig, it began to be accepted that the nutrient substances of plants were inorganic. This utterly transformed one basic belief about agriculture, namely that the production of food had fixed limits. It was now accepted, in contrast, that no such limits applied.
    T HE D ISCOVERY OF THE C ELL
     
    At much the same time as the discovery of the benzene ring and the understanding of the nature of fertilizer, German biologists were also at work on the discovery of the cell. This, the idea that all forms of life are composed of “independent, but cooperative” units that we now call cells ranks as one of the seminal discoveries in biology. 25 The first