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Crop Science Abstract -

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


This article in CS

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

    * Corresponding author(s):
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  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.