N2(C2H2)-fixation in early stages of a primary succession on a reclaimed salt marsh

Nitrogen fixation activity was determined for Lotus tenuis. Medicago lupulina and Trifolium pratense . The three species grew in clones in grassland in an area reclaimed from brackish water in the 1940s. The N₂C₂H₂]-fixation was measured in soil cores throughout 1974 and 1975. From cores taken in dense and uniform stands of the species, the yearly N₂C₂H₂]-fixation at maximum cover was estimated. L. tenuis fixed about 4 g N m^?2 yr^?1 (area with max. cover 130%), i.e. 30–56% of its requirement. Both M. lupulina and T. pratense fixed about 7 g N m^?2 yr^?1 (maximum cover 37% and 80%) i.e. 67% of their N-requirement. Average N₂C₂H₂]-fixation for the whole area was 0.4 g N m^?2 yr^?1, considerably less than the N-addition through rainfall.