| Summary: | The objective of this work was to study the decomposition of five species of blue-green algae under varying environmental conditions in soil and to examine the availability of nitrogen and other nutrients supplied through the growth of blue-green algae to rice growing in pots. In the initial phase attempts were made to grow the blue-green algae on nutrient solution and culture conditions were tested to provide optimum growth. The results of pot experiments showed that growth of all five species of blue-green algae produced an increase in dry matter yield of rice significantly higher than the controls but for four species the yield was less than the lowest addition of fertilizer nitrogen. The fifth species, Anabaena variabilies produced the highest yield in pots supporting blue-green algae but it was lower than the best yields obtained by addition of fertilizer. There was little difference in yield produced by the two fertilizers, ammonium sulphate and urea, and both increased yield with increasing addition up to the third rate (90 mg N pot-1). Nitrogen addition influenced the nutrient content of the dry matter but the growth of blue-green algae appeared to cause a small but not significant competition for nutrient uptake.
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