Nitrogen Fixation by Algae in Fescuegrass Soil Crusts

Soil crusts and subsoil samples of different ages of tall fescuegrass ( Festuca arundinacea Schreb.) were collected and analyzed for N, C, and acetylene reduction. Total N and C in the crust was 0.18% and 2.76%, respectively, in 4‐year old soil crust as compared to 0.06% and 0.67%, respectively, in fallow soil. The amount of acetylene reduction after 5 days' incubation was 13.77 µmole/flask (9.6 cm 2 ) for the 4‐year‐old sod crust compared to 3.06 µmole/flask for the fallow control. Ammonium nitrate reduced and liming increased N fixation in the crust. Nitrogen fixation in the crust was highest at 55% shade. Blue‐green algae present in the crust were Anabaena, Nostoc, Syctonema , and Oscillatoria . Greater nitrogen fixation occurred when moss ( Bryum sp.) was present in crust.