Johann August Ludwig Wilhelm Knop (28 July 1817 – 28 January 1891) was a German agrochemist and, together with Julius von Sachs, co-founder of modern water culture due to his pioneering experiments with the cultivation of crops in nutrient solutions.
Alongside Julius von Sachs, he identified nitrogen, phosphorus, sulfur, potassium, calcium, magnesium, and iron as essential elements for plant nutrition.
[2] Knop and von Sachs pioneered the use of standardized nutrient solutions in experimental plant physiology.
[3] Knop's solution, which consists of his four-salt mixture and traces of an iron salt,[4] is still commonly used in plant biology today.
[6][7] For Knop, the cultivation of crops in nutrient solutions was primarily a method for discovering scientific laws, a principle shared by Dennis Hoagland.