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Nitrogen Fixation by Algae in Fescuegrass Soil Crusts¹

ABSTRACT

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 cm²) 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.

¹ Contribution from the Dept. of Agronomy, Univ. of Georgia Agricultural Experiment Stations, Athens, 30602.

² Graduate Assistant and Professor of Agronomy, respectively.

Received for publication November 4, 1974. Accepted for publication February 12, 1975.