Assessment of the Possibility of Increasing Phosphorous and Potassium in Fish Tonic by Natural Minerals

Abstract

Fish tonic, a liquid fertilizer derived from fermented fish waste, is valued for its nutrient content and microbial benefits. However, its typically low phosphorus (P) and potassium (K) levels limits its effectiveness as a balanced fertilizer. Meantime, sugar source is more effective to enhance the microbial activities during the process. This study aimed to evaluate the potential to enhance P and K levels in fish tonic. A two factor factorial experiment in a completely randomized design (CRD) was used, with three replicates per treatment. The first factor was the sugar source (brown sugar and sakkara), and the second factor was the P and K source (spent wash + Eppawala rock phosphate ERP, spent wash + feldspar, spent wash + ERP + feldspar, spent wash, water). Each treatment mixture containing 2 kg of fish, 1 kg of sugar source, 650 ml of spent wash or water, and ERP and feldspar (either 200 g of ERP or feldspar alone, or 100 g of each when combined). Fermentation was carried out anaerobically for 34 days, followed by three months of storage with monthly analyses for pH, electrical conductivity (EC), and Nitrogen% (N), Phosphorous% (P), and Potassium% (K). Data were analyzed using ANOVA, and means were separated using Duncan’s Multiple Range Test at p<0.05. Results revealed that, pH remained acidic (3.97-4.36), while EC ranged between 4.29- 6.08 dS/m during storage. Total nitrogen content ranged from 0.12% to 1.42%, showing gradual increase during the storage but not significantly different (p>0.05). In contrast, P and K contents showed significant (p<0.05) difference among the K and P source during the third month, with the higher P and K levels recorded in spent wash+ERP (0.65%, 0.11%), spent wash+feldspar (0.64%, 0.12%), spent wash+ERP+feldspar (0.68%, 0.13%), spent wash (0.60%, 0.08%) respectively. These results indicate that combining ERP and feldspar with spent wash effectively enhances P and K content in fish tonic, underscoring its potential as a well- balanced liquid fertilizer for sustainable farming.