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Abstract SUMMARY Tne present study was carried out to investigate the effect of some ecological factors on the growth and N2-fixation of both AzalIa pinnata and Azolla filiculoides. The plan of work included the following experiments: study for growing of ~ pinnata and A. filiculoides to define the growth curve of each species, and to investigate the effect of nitrogenous compounds, viz., urea and ammonium sulphate at concentrations of 0, 10. 20, 30. 40. and SO ppm N on the growth and N2- fixation of each AzalIa. The study also included the effect of salinity in the form of sodium , chloride and sodium sulphate at concentrations of 0, 100, 200, 500, 800, 1000 and 1500 ppm on the growth and N2- fixation of both the two species of AzalIa. The effect of illumination periods, viz.~ 24, 12, 6, 0 hrs. on the growth and N2- fixation of each species of AzalIa was also investigated. Further, the effect of different rates of nitrogen and A. pinnata application on the rice yield was also investigated as compared with different levels of urea-Nt viz .• 0, 20. 40 and 60 kg N/ fed. In this experiment. two procedures of application of A. pinnata in the soil namely, surface inoculation and soil incorporation were employed. The results could be summarized as follows : 1- Data of comparative study experiment clearly indithat there is a positive relationship between the and the incubation period up to 36 days for A. cated growth - 85 - Qin~~tA and 28 days tor A. fi~i~~~9j~e~ after which the ~rowth yield decreased. Nitrogen content of both Azolla was found to follow the same trend similar to that of the dry weight. The results of nitrogenase activities of the tested Azolia species were not constant and exhibited fluctuations during the incubation periods. It could be noticed that A. pinnata and ~ filiculoides exerted maximum N2 fixing capacity on the 28th and 11th days of incubation respectively after which the nitrogenase activity decreased. 2- Two nitrogenous compounds, viz .• ammonium sulphate and urea were used to investigate their effect on the• growth, of both Azolla species. The data showed that the highest increase was recorded on the 21th day of incubation in presence of 50 ppm urea-N of A. pinnata and A. filiculoides. The highest biomass was obtained when 50 ppm urca-N- was used. The rate of increase was higher in case of urea-N as compared with NH.-N. The data indicated that the highest nitrogen accumulation by both A. pinnata and ~ tiliculoides can be obtained on the 21th day of incubation in presence of 50 ppm nitrogen either in the form of NH.-N or urea-No The effect of addition of NH.-N and urea-N on nitrogenase activity indicated -that both NH.-N and urea-N has a depressive effect on the nitrogenase activity, and the depressive effect of both forms of nitrogen was increased by increasing nitrogen concentration. - 86 - 3- In this experiment sodium chloride and sodium sulphate at different concentrations, namely, O. 100, ZOO. 500, 8UO, 15UO ppm were used. Results indicated that the growth of both Azoll~ species in terms of fresh and dry weights, decreased by increasing NaCI and NaS SO. concentrations. A. filiculoides was found to be relatively resistant to high concentrations of both salts, i.e., 1000 and 1500 ppm as compared to ~ ~nnata. The growth of A. ~innata was comnpletely inhibited on the Zlth day of incubation in the presence of 1000 and 1500 ppm of both salts. f The values of the total fixed nitrogen by both Azolla species behaved similarly in accordance with the dry matter content, the depression of N-accumulation was increased by increasing salt concentration, such effect was more pronounced in the case of ~ pinnata especially at the concentrations of 1000 and 1500 ppm. The maximal nitrogenase activity of both Azolla species was detected in the absence of salts. By increasing NaCl or Na2S0. concentration the nitrogenase activity decreased. 4- In this experiment illumination periods namely, 24. 1Z, 6 and a hrs. of light were used. results showed that the growth of A. pinnata and Azolia filiculoides was stimulated by exposing the Azolla fronds to 12 brs. of light followed by 12 brs. of dark the highest increase was recorded on the - 87 - ~lth day of incubation. More incubation of Azolla fronds in the dark for 18 hrs. resulted in sharp decrease in the dry weight. The growth of both ~zolla species was completely inhibited on the 21th and 28th day when incubated in complete darkness. The N2- fixing capacity was highest when both Azolla species were exposed to 12 hrs. light followed by 12 hrs. dark. The N2- fixation of both Azol1a species reduced sharply when exposed to 6 hrs. of light. At complete darkness the N2-fixing capacity was completely inhibited by both Azolia species. The maximal nitrogenase activities of both Azolla species was detected when they were exposed to 12 hrs. of light followed by 12 hrs. of dark. By increasing dark period the nitrogenase activities were decreased and ceased in complete darkness. 5- Data of rice experiment showed generally that the incorporation of ~ pinnata in the soil was better for obtaining higher values of rice growth parameters than the surface incubation. The maximum values of the rice growth parameters were obtained by incorporating 40 kg/ fed. of Az~lla-N in presence of 20 kg/ fed. of urea-No |