Enhancing nutrient retention in fermented bio-extract using biochar derived from oil palm empty fruit bunch

The application of fermented bio-extract (FB) to promote plant growth is increasingly adopted in organic agriculture. However, nutrients in FB are readily lost through leaching, limiting their effectiveness. This study investigated biochar derived from oil palm empty fruit bunches (EFB) as a carrier for retaining nutrients from an FB produced from seafood processing waste. The EFB biochar contained 1.48% N, 0.72% P, and 1.68% K, whereas the FB contained 1.39% N, 1.03% P, and 0.64% K. Nitrogen adsorption increased with FB concentration and contact time, approaching equilibrium after 60 min. After enrichment, the nutrient contents of the biochar increased to 3.18% N, 2.30% P, and 3.03% K. Immersion experiments showed that FB-enriched EFB biochar retained significantly higher amounts of N, P, and K than untreated biochar during the first 6 h. Pot experiments further demonstrated that FB-enriched EFB biochar significantly improved the growth and biomass of Chinese kale compared with cattle manure, despite supplying substantially less nitrogen than urea at the same application rate. These findings indicate that EFB biochar can serve as an effective nutrient carrier with potential as a slow-release organic soil amendment while simultaneously valorizing agricultural waste for sustainable crop production.