AbstractThe acetylene‐reduction method was used to estimate the fixation of atmospheric nitrogen by non‐symbiotic micro‐organisms in soils from England and Wales. Significant fixation was found only in the surface horizon of the soil (0–1 cm) and was much higher in the light than in the dark. The highest rates were found with samples having a well‐developed surface film of blue‐green algae and were from 6 to 10 g ha−1N per h. Generally, rates were very much lower. The addition of fertilizer nitrogen at 100 kg ha−1markedly reduced N fixation by b