Influence of different concentrations of ammonium phosphate on nitrogen assimilation of red seaweed Kappaphycus striatus

Abstract

Eucheumatoid farming is among the most popular source of livelihood for coastal dwellers, especially in the southern Philippines. Kappaphycus and Eucheuma are the two major cultured eucheumatoid species. However, seaweed farmers have been experiencing low seaweed production for the past years. The slow growth of Kappaphycus spp. in the farm is linked to extensive farming, causing nutrient depletion in the seawater. Hence, seaweed farmers in the province of Tawi-Tawi, southern Philippines, enrich their seaweeds, Kappaphycus striatus, with a wide range of inorganic nutrient solution concentrations with an average of nearly 9 g L⁻¹. To provide standard concentration (g L⁻¹) of inorganic nutrient solution for soaking before farming the seaweed, this study investigated nitrogen assimilation using the Kjeldahl method. Treatments were the concentrations of commonly used inorganic fertilizer [ammonium phosphate, (NH4)3PO4] dissolved in filtered seawater namely; T1 = 0 g L⁻¹ as control, T2 = 3 g L⁻¹, T3 = 6 g L⁻¹, and T4 = 9 g L⁻¹. Results showed that the total nitrogen (%) of T4 (0.68±0.01) and T3 (0.59±0.07) were significantly higher (p<0.05) than T2 (0.48±0.02) and T1 (0.46±0.02). This suggests that using inorganic nutrients as enrichment to K. striatus at a concentration of 6 or 9 g L⁻¹ is effective for obtaining high nitrogen assimilation. Therefore, considering the cost-effective inorganic nutrient enrichment practice, this study recommends using 6 g L⁻¹ of inorganic nutrient concentration to help seaweed farmers boost production by improving the growth performance of K. striatus, especially when planted in nutrient-depleted farms.