ABSTRACT
Liebig fought the idea that humus, a product of the decay of plants contained in the mould, might be absorbed by the roots and serve as food for plants by providing them its carbon. In reality, this involved a complex mix from various sources, which the chemist had to analyze.
- The carbon in plants does not come from the soil: 1) Ulmic acid, practically insoluble, is not absorbed by the roots. 2) If it is then assumed that it can be absorbed in the form of salt (lime ulmate), the calculation of the quantities of basic oxide available for this leads to a weight of pine wood that is derisory compared with the wood actually provided by the forest. The same holds for a field of wheat. 3) The calculation of the quantity of ulmic acid introduced by rain water in the most favourable circumstances gives an even more ridiculous result. 4) Furthermore, equal areas of land (forest, prairie, grains) produce equal amounts of carbon.
- Thus, carbon in plants comes from the atmosphere. Oxygen is ceaselessly consumed by respiration and combustion on a grand scale. Vast quantities of carbon dioxide are produced. Nonetheless, the quantities do not vary; there is a relationship between them. Animal life depends on plant life. Cultivation improves the health conditions of a country.
