Humus: latent phase and reality

The evolution of the concept of humus was in large part dependent on the development of the modern agriculture. This concept derived from the very old practice of manuring and, after a long period of empirical application, was first theorised by Albrecht Thaer, who recognised the organic and inorganic content as the nutritional elements of humus. The role of humus as nutrient was challenged by Carl Sprengel and Justus Liebig, who opposed successfully the mineral theory to the theory of humus. The research in the property of humus, however, continued thanks to agronomists and agricultural chemists during a period in which the mineral theory was consolidated by the first experiments of the hydroponic cultures performed by Julius Sachs and Wilhelm Knop, but several outstanding chemists and microbiologists continued the work initiated by Thaer, giving humus full physicochemical identity and function. In this context shone the figure of Selman Abraham Waksman, whose work was of fundamental importance to the subsequent research in humus, which is still in progress.