NITROGEN FIXATION IN SOIL CRUSTS OF TALL FESCUE SODS

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Abstract
Soil crusts under tall fescuegrass (F. arundinacea Schreb.) were studied for possible N2-fixation. Crust samples were collected and analyzed for total N, following the growing of fescue for periods of time up to 6 yr. N content of soil crust increased from 0.03% in fallow soil to 0.246%, and below the crust, to a 15-cm depth, N increased from 0.027% to 0.38% after 6 yr of grass. This is .apprx. 54 kg/ha annual N increase for the grassland soil. Soil crusts with moss (Bryum) exhibited higher N2-fixation (C2H2 reduction) than crusts without moss. Moss samples from beneath fescuegrass demonstrated higher N2-fixation than moss without fescue cover. The N content of the moss under fescue was also higher on highly acid soil than moss without cover. N2-fixation by the soil crust was less at pH 5 than pH 6 or 7 at the first sampling. After moss had grown sufficiently to give good soil cover, soil pH had much less effect on N2-fixation, indicating that blue-green algae on leaf scales of moss were possibly contributing most of the fixed N.

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