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Wilhelm Knop

Wilhelm Knop

Wilhelm Knop (28 July 1817 – 28 January 1891) was a German agrochemist and co-founder of modern water culture. Alongside Julius von Sachs, he identified nitrogen, phosphorus, sulfur, potassium, calcium, magnesium, and iron as essential elements for plant nutrition. Knop and von Sachs pioneered the use of standardized nutrient solutions in experimental plant physiology.

Knop's solution, which consists of his four-salt mixture and traces of an iron salt, is still commonly used in plant biology today. Dennis Robert Hoagland and Daniel Israel Arnon proposed that Sachs' solution (1860), Knop's solution (1865), Pfeffer's solution (1900), and Crone's solution (1902) should be supplemented with boron, manganese, zinc, copper and molybdenum for best results with water culture experiments.

For Knop, the cultivation of crops in nutrient solutions was primarily a method for discovering scientific laws, a principle shared by Dennis Hoagland. For determining the effectiveness of mineral fertilizers, he regarded the field experiment as the authoritative method of investigation. The names of Hoagland and Knop are commonly used as a brand for an innovative product, namely the Hoagland and Knop Medium, which has been specially formulated for plant cell, tissue and organ cultures on agar.


  • Heinz Walter (1980), "Knop, Wilhelm", Neue Deutsche Biographie (in German), vol. 12, Berlin: Duncker & Humblot, pp. 214–215

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