INFLUENCE OF PHOSPHORUS AND POTASSIUM SOURCES ON THE GROWTH, NITROGEN FIXING ACTIVITY AND AMMONIA EXCRETION OF SALT TOLERANT CYANOBACTERIAP. AMSAVENr AND S. KANNAIYANAbstract In view of the global crisis of demand for the replacement of chemical fertilizer with biofertilizer and maintain the soil aggregation properties of salt affected soil, an emphasis has been made to improve the growth, nitrogen fixing activity and ammonia excretion of salt tolerant cyanobacterial cultures. Three salt tolerant cyanobacterial cultures viz., Anabaeria-TR-52-ST1, Nostoc-BS-60-ST2 and Westiellopsis-TR-5- ST3 isolated from saline and soclic soils of Tamil Nadu were employed in this study with an objective to evaluate the effect of phosphorus (single super phosphate and rock phosphate) and potassium (commercial murate of potash and potassium sulphate) on growth, nitrogen fixing activity and ammonia excretion of these algal cultures. The results revealed that both phosphorus sources viz., single super phosphate (SSP) and rock phosphate have positively influenced the growth, nitrogen fixing activity and ammonia excretion of all the three algal cultures. Compared to rock phosphate, single super phosphate at 10 and 20 ppm has accelarated the growth, nitrogenase activity and ammonia excretion of algal cultures. Among the three algal cultures, Westiellopsis-TR-5-ST3 has registered higher parameters mentioned above than the other two cultures. Of the two potassium sources tested in this study, potassium sulphate (K2 SO4) have increased the growth, ammonia excretion and nitrogenase activity of all the cyanobacterial cultures. The results suggest that addition of phosphorus and potassium nutrients trigger the growth, nitrogenase activity and ammonia excretion of salt tolerant cyanobacterial cultures. Hence, these nutrients can be amended to the normal growth medium for the mass multiplication of cyanobacterial cultures.
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