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This article in CS

  1. Vol. 29 No. 4, p. 1033-1037
    Received: July 22, 1988

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Phosphorus Requirement of Azolla pinnata: Effects of Low Concentrations on Growth and Nitrogen Fixation

  1. R. N. Sah 
  1. Dep. of Agronomy and Range Science, Univ. of California, Davis CA 95616



There are conflicting reports about the critical P requirements for growth and N2 fixation of Azolla pinnata-Anabaena azollae association (azolla). This study was conducted to determine critical concentrations of media P and tissue P for optimum growth and N2 fixation of azolla. Continuous flow-through experiments using media-P levels ranging from 0 to 500 μM were conducted in a greenhouse. There were no differences in growth and N 2 fixation of azolla grown at media-P concentrations between 0.5 and 500 μM. Azolla initially high in tissue P (13 to 15 g P kg-I dry wt.) grew in the Pfreemedium at the optimum rate for about I0 d. For the optimum growth of azolla, media P between 0 and 0.5 ~M and about 1.0 g tissue P kg-1 dry wt. appeared to be the critical concentration. The critical medium-P concentration was significantly lower than the reported value, 2 ~M. Nitrogen fixation correlated with growth, but tissue-N and P concentrations did not. Increasing media-P concentrations decreased P utilization efficiency. Results suggest that the difference between deficient and sufficient media-P and tissue-P levels may be very narrow.

Contribution of the Dep. of Agronomy and Range Science, Univ. of California, Davis. This research was supported by a grant from USAID under Indo-US Science and Technology Initiative.

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Copyright © 1989. Crop Science Society of America, Inc.Copyright © 1989 by the Crop Science Society of America, Inc.