Persistence of azolla in lowland rice ecosystem

Azolla is a freshwater fern which has the ability to fix nitrogen (N) through its symbiotic relationship with Anabaena azollae. Numerous studies conducted have demonstrated its effectiveness as biofertilizer in rice production. Despite the effort of the Philippine government to promote Azolla as biofertilizer in rice production in the 1986, only very few rice fields where Azolla could be found nowadays. The environmental conditions and growth characteristics such as growth rates, sporulation index and germination rate, contributing to the continuous existence of azolla in a specific location is the subject location is the subject of the present study at PhilRice particularly on the reasons for the persistence of Azolla in Brgy (Barangay) Taytay, Majayjay, Laguna [Philippines]. The study also provides information on the pre-condition in using spores as inoculum in the rice paddies with the objective of making azolla a stable component of lowland rice environment. The environmental condition and cropping system of rice farms in Majayjay was observed to be favorable to induce sporulation and complete the growth cycle of Azolla which leads to its subsistence. The vegetative and reproductive cycle of Azolla sp. collected from Brgy. Taytay was studied in the Azolla nursery and laboratory at PhilRice Los Baños and in the field for two cropping seasons. In two cropping season of rice, the azolla sporulates four times. Each sporulation produces 15,000 to 17,500 zygote/sqm. The presence of floodwater provides the conditions for the germination and development of sporophyte until it becomes fully developed plant within the period of one month. When azolla can no longer undergo fragmentation due to growth limitating factors, the plant matures to produce spores. The young azolla would continue to grow and cover the one square meter for 2 to 3 days. The azolla sporeling can produce spores at 15 to 20 days given the environment is favorable.