Career
Overgaard Nielsen was a soil ecologist, specializing in soil nematodes and Enchytraeidae. He investigated the role of the soil microfauna in the decomposition of plant litter and recycling of nutrients in ecosystems. He was a visiting scientist with Charles Elton at Oxford University in 1950-1953.
He was then employed at the Mols Laboratory under Aarhus University.
In 1964, he was appointed professor of zoology at the University of Copenhagen. He was the first Editor-in-Chief of the scientific journal Oikos (1949-1965).
