Comparative Effects of Vermicompost and NPK Fertilization on Growth, Heterocyst Frequency, and Protein-Lipid Accumulation in Azolla microphylla

Abstract

Azolla sp. is a rapidly growing aquatic fern valued as a nitrogen-rich biofertilizer and sustainable feed source. Its nutritional value is attributed to its high protein content, essential lipids, vitamins, and minerals, which contribute to improved animal nutrition. Ecologically, the plant maintains a permanent symbiotic association with nitrogen-fixing cyanobateria, enabling its adaptation to diverse and extreme environments. This study compared the effects of vermicompost (VC) and NPK (15:15:15) fertilizers at five concentrations (0–1000 ppm) on biomass accumulation, heterocyst frequency, and protein–lipid content of A. microphylla under greenhouse conditions. Relative growth rate (RGR) was calculated every three days, heterocyst frequency was quantified microscopically, and protein/lipid contents were determined using AOAC (2016) methods. Results showed that VC treatment significantly enhanced biomass yield (RGR = 0.23 at 750 ppm, p < 0.05), sustained higher heterocyst frequency across concentrations, and produced greater protein (24.31 ± 0.60%) and lipid (13.71 ± 0.08%) contents compared to NPK (17.62 ± 0.80%, 8.53 ± 0.05%, respectively). In contrast, NPK promoted growth only at 250 ppm and inhibited heterocyst formation and nutrient accumulation at higher concentrations. These findings indicate that VC provides a balanced, slow-release nutrient supply that supports both growth and symbiotic nitrogen fixation, highlighting its potential to enhance Azolla production for biofertilizer and feed applications.