Influence of different phosphorus management strategies on the sporulationand growth of Azolla

Phosphorus at the recommended dose of 10 kg P2O5 ha(-1) divided between thr ee equal applications, one on each of 0, 7 and 14 d after Azolla inoculatio n (DAI), increased biomass production but sporulation was invariably inhibi ted. Of the different options tested, lowering the phosphorus application r ate to 4-8 kg P2O5 ha(-1) significantly improved sporulation in A. microphy lla (strain 202) but there was a substantial reduction in biomass productio n. On the other hand, changing the schedule of phosphorus application from 0, 7 and 14 DAI to 0, 3 and 6 DAI did not hamper biomass production and imp roved sporulation frequency and sporocarp number in A. microphylla (strain 202), A. caroliniana and A. pinnata. It was comparable to the no-P treatmen t for the number of sporocarps, with slightly lower sporulation frequency. In these species, the sporulation frequency and sporocarp number of Azolla enriched with 30 or 60 kg P2O5 ha(-1) and then grown without any further ad ded phosphorus were higher than those of unenriched Azolla grown with 10 kg P2O5 ha(-1) and mostly comparable to those of Azolla grown without phospho rus. Foliar spray of 2.5 mug ml(-1) gibberellic acid (GA) solution (7 DAI) along with the application of 10 kg P2O5 ha (split between 0, 7 and 14 DAI) to unenriched Azolla increased the sporulation frequency and number of spo rocarps in A. microphylla (strains 202 and 203), A. caroliniana and,A. pinn ata, not only over that of phosphorus application alone but also over the u ntreated control. Combining the use of P-enriched Azolla (A. microphylla st rains 202 and 203) with application of GA was more effective for increasing sporulation than was the use of P-enriched Azolla without GA,, or applicat ion of phosphorus plus GA to unenriched Azolla.