Justus von Liebig, a German chemist, put forward the Law of the Minimum in 1840. It states that a plant's growth is not decided by how much of every resource is available overall, but by whichever single resource is scarcest, the "limiting factor".
This idea is often explained using "Liebig's barrel", where the shortest stave, representing the most limiting nutrient, determines how much water the barrel can actually hold no matter how tall the other staves are.
Arnon, Dokuchaev and Bousingault made other important contributions to agricultural and soil science, but this particular law belongs to von Liebig.