Aims Nitrogen deficiency in eco-engineered technosol from iron (Fe) ore tailings limits the productivity of colonising soil microbes and pioneer plants, which are critical to further development of the technosol. Symbiotic biological N 2 fixation may be a strategy to supply N in the moderately alkaline early technosols since native legumes such as Acacia auriculiformis are tolerant of saline and alkaline soil conditions as tho...