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Nitrogen Fixation by Azotobacter paspali in Association with Bahiagrass (Paspalum notatum)¹

ABSTRACT

Establishment of Azotobacter paspali in the rhizosphere of Paspalum notatum grown in sand was consistently successful only with tetraploid varieties of the grass when glucose was added at the time of inoculation. Increases in the nitrogen content of the roots and in the total nitrogen content of the sandplant system were associated with successful Azotobacter colonization. These increases were significant at p < 0.05. There was no evidence for improved growth or for nitrogen gains in the above-ground portions of the plants resulting from A. paspali establishment.

Soils containing tetraploid P. notatum and A. paspali showed considerable nitrogen fixation, as measured by acetylene reduction. The nitrogen gains appeared to be a consequence of growth of photosynthetic microorganisms, since all fixation ceased when soils were incubated in the dark.

¹ Agronomy paper no. 902. Contribution from the New York State College of Agriculture, Department of Agronomy, Cornell Univ., Ithaca, N.Y., 14850. This study was supported in part by a Ford Foundation grant.

² Research Assistant and Professors of Soil Science, respectively.

Received for publication July 22, 1970. Accepted for publication November 19, 1970.