Humus theory
The humus theory is a theory according to which a plant feeds on the humus . The fertility of a soil was equated with its humus content, the depletion of humus was seen as the main cause of the soil becoming sterile.
The humus theory was further developed by the universal scholar Jean-Henri Hassenfratz ( 1755 - 1827 ) in such a way that a plant does not take its carbon needs from the air, but rather from the darkly colored humus substances in the soil and apart from the humus substances only needs water to grow. This was the result of his observation that plants grow better on deep soils with a lot of humus and that the humus is, as it were, consumed by the plants. The purpose of fertilization would be to enrich the soil with humus-forming substances (plant and animal products).
This humus theory development was picked up and spread by:
- the physician Albrecht Thaer in his book "Principles of Rational Agriculture", published in 1809 , for which the inorganic substances were only irritants, but not nutrients that were indispensable for plant development,
- and the agronomist Johann Burger in his "Agricultural Textbook".
The humus theory was refuted by the mineral theory and the law of the minimum by Carl Sprengel , both of which were later propagated by Justus von Liebig from 1842 . See also the historical development of plant nutrition .
literature
- Manual of Plant Physiology - Encyclopedia Of Plant Physiology IV. Reprint, Springer-Verlag, ISBN 978-3-642-94730-8 , limited preview at Google Books .