The Utricularia-cyanaphyta and Azolla-anabaena associations: their ecology, nitrogen fixation rates, and effects as biofertilizers on rice.
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Date
1996
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University of Dar es Salaam
Abstract
A survey of Dar es Salaam, Coast, and Morogoro regions in Tanzania showed that Utricularia-Cyanophyta was more widely distributed and abundant than Azolla-Anabaena. The latter association was only found in one permanent lake, while the former was found in one permanent lake and several seasonal ponds and rice fields, demonstrating its ability to regenerate from seeds. The only species of Azolla found was A. nilotica. U. inflexa, U. reflexa, and U. gibba were found abundantly associated with a variety of blue-green algae. Water depth, water movement, and biotic factors were important in limiting the distribution of these associations. Two experiments were conducted (in outdoor cement tanks enclosed with wire mesh) to assess and compare the effectiveness of Azolla nilotica-Anabaena and Utricularia gibba-Cyanophyta as biofertilizers on rice grown in soil taken from three local paddy fields. Though the shortest doubling times during initial stages of growth were similar for Azolla-Anabaena and Utricularia-Cyanophyta, being 2.0 and 2.3 days, respectively, the former showed significantly faster overall growth rates and greater maximum biomass accumulation (the highest being 90g fresh weight m-2 day-1 and 2.9 kg m-2, respectively) than did the latter (the highest being 36 g m-2 day-1 and 1.7 kg m-2, respectively). Utricularia gibba was shown to play an important role as a substrate for the support of growths of blue-green algae, particularly Gloeotrichia, Aulosira, and Lyngbya. Azolla-Anabaena fixed nitrogen (reduced acetylene) in situ at significantly higher rates than did UtriculariaCyanophyta, showing maximum rates of 695 and 114 nmol C2H4 g-1 fresh weight h-1, respectively. Rates in Utricularia-Cyanophyta were significantly correlated to the abundance of associated blue-green algae. Both biofertilizers resulted in increased rice height and number of tillers per hill in comparison with control tanks where no biofertilizer was applied. Grain yield increased by 10-103% (varying among soil types and between experiments) with the application of Azolla-Anabaena and by 13-107% with the application of Utricularia-Cyanophyta, while straw yield increased by 1-23% and 1-35%, respectively. In most cases, differences over controls were significant or very significant. There was no consistent difference between the effectiveness of Azolla-Anabaena (already proven effective in other countries] and Utricularia-Cyanophyta (demonstrated for the first time as an effective biofertilizer). It is suggested that the comparable effectiveness of the latter, despite its much lower nitrogen fixation rates, may be due to the release of growth promoting substances by the variety of associated blue-green algae. Both associations are recommended as effective biofertilizers for application on rice in Tanzania.
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Keywords
Utricularia, Anabaena azollae, Biofertilizers, Tanzania, Dar es Salaam, Morogoro regions
Citation
Wagner, G. M. (1996). The Utricularia-cyanaphyta and Azolla-anabaena associations: their ecology, nitrogen fixation rates, and effects as biofertilizers on rice. Doctoral dissertation, University of Dar es Salaam. Available at (http://41.86.178.3/internetserver3.1.2/detail.aspx?parentpriref=)