Browsing by Author "Wagner, Gregory Miles"

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    The ecology and nitrogen - fixing capacity of freshwater blue-green algae in selected localities in Tanzania
    (University of Dar es Salaam, 1983) Wagner, Gregory Miles
    In the vicinity of Dar es Salaan and near the town of Zanzibar, 23 taxes belonging to six families of the Cyanophyta were identified, In a survey of streams, ponds, lakes, and fields, many taxa were found to be ubiquitous. In an ecological study in a rice field, certain environmental parameter, Cyanophyta population characteristics, and in situ nitrogen-fixation rates were measured concurrently over time. Total filamentous algal ubunctance (measured using a direct microscopical method) reached a peak of 0.53 mm3cn-2 at the end of the principal rainy season. Forms of the genera Oscillatoria Lyngbya, Anabaena, and Nostoc were dominant. Nitrogen-fixation (measured using the acetylene reduction technique) occurred at I3,6 nmol C2H4 cm-2h-1 at the end of the principal rainy season and 1.1 nmol G2H4 cm- 2h-1 during the cool dry season. Controls indicated that the Cyanophyta were primarily responsible for the nitrogen-fixation. Soil moisture was the the key factor controlling seasonal variation in algal abundance. Rainfall and shading by rice and weeds were important through their effect on soil rnoisture. Tillage of the soil caused a major disturbance of legal growth. Seasonal variations in solar radiation, temperature, soil temperature, pH, cation exchange capacity, and exchangeable K+ were relatively unimportant. There was a very significant correlation tween heterocystous algal abundance and nitrogen-fixation. Forms of Aulosira and Cylindrospermum fixed nitrogen in situ at 161.2 and 4l.6 nmol C2H4 cm-2n-1, respectively, indicating their promising potential as biofertilzers. Blue-green algae, particularly Anabaena were found to be consistently associated with Utricularia inflexa. Epiphytic blue-green algae both inside the traps and on the outer surfaces of the plant fixed nitrogen in situ. The association showed a. nitrogen fixing capacity of 20'12 nmol C2114 g(dry wt.) 1-h-1. Recommendations are given concerning the development of free-living algae and the Utricularia -Cyanophyta association as bio fertilizers in agriculture in Tanzania.
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    The Utricularia-cyanaphyta and Azolla-anabaena associations: their ecology, nitrogen fixation rates, and effects as biofertilizers on rice.
    (University of Dar es Salaam, 1996) Wagner, Gregory Miles
    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.