Iron Fertilization Increases Seaweed Yield
In recent years, there has been a decline in the productivity of red seaweeds in the Sulu Sea where the bulk of the production comes from. The drop is attributed to many factors such as genetic deterioration (slow growth), lack of nutrients, and adverse environmental conditions.
The application of chemical fertilizers such as ammonium nitrate and ammonium sulfate is practiced in China and Japan for seaweed culture in coastal waters. In the Philippines, seaweed farmers do not apply fertilizer. No studies on the use of fertilizers for increasing growth of seaweeds in coastal waters have been reported yet.
Recently, studies on the effect of iron fertilization on the growth of the red seaweed, Kappaphycus alvarezii, and the green seaweed, Gracilaria heteroclada, were conducted in the coastal waters of Batangas and Misamis Oriental, respectively. The studies were conducted by scientists of the Philippine Council for Aquatic and Marine Research and Development, Aquatic Biosystems and Xavier University in the Philippines, and Nihon University in Japan with support from the Japan International Marine Science and Technology Federation.
Results of the studies on the red seaweed published in the Asian International Journal of Life Sciences showed that yield of the seaweed was significantly increased by 30 percent with the application of Ocean Green, a commercial fertilizer containing 20 percent fenous sulfate produced in Japan. The fertilizer was applied through perforated plastic bags suspended in the floating rafts (10 x 5 meters each in area) with monolines for attachment of the cultured seaweed. The fertilizer application rate of 2 kg per week per raft gave the highest yield compared to that of the control (no fertilizer) and that of the treatment with a lower application rate (1 kg) after 60 days of culture. Application of the fertilizer was also found to be cost-effective.
For the study on the green seaweed, the application of Ocean Green at 0.5 kg per floating cage (5 x 2 x 0.4 meter) per week gave the highest yield which was 22 percent more than that of the control and 15 percent than that from the treatment with the lower application rate (0.25 kg) after 62 days of culture.
An interesting observation made from the studies was that with incidents of “ice-ice”, a disease of seaweeds caused by adverse environmental conditions such as high water temperature and low salinity, the plants that were fertilized with Ocean Green apparently had better resistance to the disease than those of the control.
Iron is an essential element for the production of chlorophyll, a compound needed for photosynthesis (food production of plants with sunlight), and other important biological processes. It is present in seawater in very limited amounts.
For more information on the above mentioned studies, readers may contact the PCAMRD thru e-mail address pcamrd@laguna.net.
