Inorganic nutrient enrichment of seaweed Kappaphycus: Farmers’ practices and effects on growth and ice-ice disease occurrence

Abstract

Inorganic nutrient enrichment (INE) is an emerging practice among seaweed farmers in Sibutu, Tawi-Tawi, southern Philippines, as a response to the slow seaweed growth and as a control measure for the ice-ice disease. A survey on the practice of INE of Kappaphycus and a field experiment simulating the practice were conducted. From the 100 farmers, 83% practiced INE, 14% did not practice, and 3% stopped the practice. From those who practiced, 87% were using 16−20−0 fertilizer and 13% were using 14−14−14 fertilizer. Seaweeds were dipped into 8.82 g L−1 fertilizer solution for 5–60 s, piled up on a drying platform, covered with canvas overnight, and planted the following day. Seaweeds were hauled up 7–10 days post-cultivation for re-application of INE. Harvesting and/or mass propagating was done at 20 days post-planting. Respondents reported that this method increased seaweed growth and decreased ice-ice disease occurrence. For the field experiment, 8.82 g L−1(HC), 0.01 g L−1(LC), and 0.00 g L−1(UF) of 16−20−0 fertilizer concentrations were tested in Kappaphycus striatus farmed using the modified fixed-off bottom method. At 49 days post-planting, the growth of K. striatus in HC (3.75 % day−1) was significantly higher than in LC (1.82 % day−1) and in UF (1.56 % day−1). Ice-ice disease occurrence of K. striatus was significantly lower in HC (42.37%) than in LC (78.07%) and UF (77.72%). Higher growth and lower ice-ice disease were evident with INE; however, effects in farm environment and on carrageenan quality were also reported. Further, the use of inorganic commercial fertilizer in seaweed farm is discouraged by the Philippine National Standard. Thorough studies that will address these knowledge gaps are needed for science-based policy on regulation and management of use of inorganic fertilizers in Kappaphycus cultivation.