Application of N₂-fixing cyanobacteria nostoc sp. SO-A31 to hydroponically grown water spinach (ipomoea aquatica L.)

For this research, an application of cyanobacteria Nostoc sp. SO-A31 as a nitrogen source for the growth of water spinach (Ipomoea aquatica L.) was carried out using a modified Deep-Water Culture (DWC) hydroponic system, outdoors. A Hoagland medium was used for the growth medium, with the absence or presence of ammonium and nitrate as the nitrogen sources. A 0.7 g fresh weight biomass of 21-day-old Nostoc sp. SO-A31 was inoculated into the system. The four treatment media for this study were HA₀ (Hoagland, ammonium free+inoculant), HN₀ (Hoagland, nitrate free+inoculant), HA₀ N₀ (Hoagland, ammonium free and nitrate free+inoculant), and HI (Hoagland with ammonium and nitrate +inoculant). AB-mix and complete Hoagland media were used as controls. The result showed that water spinach cultured on HA₀ had good vegetative growth, as shown by the high yield of biomass, high number of leaves, high stem growth, and long roots. Inoculation of Nostoc sp. SO-A31 elongated the root of the water spinach plants in all treatments. The presence of Nostoc sp. SO-A31 in the complete Hoagland medium, though, caused chlorosis of the water spinach leaves. This study suggests that water spinach is a nitrate-dependent leafy vegetable.