After a short period at the university's Institute of Physical Chemistry, he worked for several years at the Agricultural Experimental Station in Leipzig-Mockern.
After having his application for habilitation blocked on political grounds in the early 1930s, he was forced to leave academia and became scientific director at the agricultural experimental station of the German agricultural chemicals company Kali Chemie [de], based in Hanover.
After his war captivity he returned to hanover, where his wife Grita and his three Children Ralf, Reiner und Uta used to live.
From the late 1920s onwards he also contributed to the theory of non-parametric statistics, and developed methods for cases involving single and two samples.
In 1933 Behrens published Mathematische Methoden fur Versuchsansteller ('Mathematical Methods for Experimenters').