On the problem of nitrogen utilization, H. Hellriegel and H. Wilfarth (1886) presented their findings at the Natural Scientists' Conference in Berlin (cited from Sachs 1887, based on a report in the Kölnische Zeitung, 1886):

"Buckwheat, rapeseed, mustard, sugar beets, oats, and potatoes obtain their nitrogen requirement entirely from nitric acid compounds (nitrates). If these plants receive nitrogen in the form of ammonia fertilizers, they can only utilize it to the extent that the ammonia is converted into nitric acid by soil microorganisms. On the other hand, peas, lupines, serradella, vetches, and clover do not rely on bound nitrogen in the soil but can obtain it from the air; they process not the bound nitrogen but the free nitrogen of the air. However, these plants can only live and process free nitrogen with the help of bacteria that produce the so-called nodules on their roots."