Algalization Technology Using a Cyanobacterium, Trichormus variabilis for Rice Production​

With the growing concern about the economic and environmental effects of continuous use of synthetic fertilizers in rice cultivation, nitrogen-fixing cyanobacteria or blue-green algae (BGA) were explored as an alternative source of fertilizers for increasing rice production. A local strain of Trichormus variabilis (Ns71Ph) was selected as a test biofertilizer because of its high growth rate and high nitrogen uptake. Its effectiveness as a biofertilizer was tested under greenhouse conditions for three consecutive experimental trials using a rice variety, PSB Rc 82, in four treatments and three replicates: T1, control (no fertilizer); T2, 100% NPK recommended rate (120-40-40 kg ha-1); T3, 50% BGA (50 kg ha-1) + 50% NPK (60-20-20 kg ha-1); and T4, 100% BGA (100 kg ha-1). Plants with 100% NPK and 50% NPK + 50% BGA had comparable grain yield, number of panicles, plant height, number of tillers, and leaf greenness during the first and third trial. Comparable phosphorus level in aboveground plant parts of all treatments in the second trial and highest potassium level in 50% NPK + 50% BGA were observed in first trial. A significant increase in soil nitrogen was noted during the third trial using 100% BGA while a decrease in extractable K was observed in 50% NPK+50% BGA in three trials. Cost and return analysis across the three consecutive trials showed that although 100% NPK obtained the highest net profit of PhP39,539.55, a reasonable return of PhP28,513.45 was attained with 50%NPK+50%BGA. This study demonstrated the feasibility of utilizing BGA as a promising biofertilizer and hopes to reduce input cost in rice production. It further recommends the conduct of actual field evaluation and a study of the long term beneficial effect of BGA to the environment.