Encapsulation of NPK in snake fruit peel biochar (Salacca edulis) and activated natural zeolite as a slow-release fertilizer for water spinach (Ipomoea reptans Poir)
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The declining of efficiency of chemical fertilizer and rapid nutrient leaching in tropical soils shows the need for affordable slow-release systems based on agricultural waste and natural minerals. Therefore, this study aims to investigate the use of biochar from snake fruit peel as a slow-release fertilizer (SRF) and evaluate the effectiveness of the combination with activated natural zeolite. The process was carried out by drying the snake fruit peel at 70°C, activating it with HNO₃ for 4 hours, and pyrolyzing it at 200°C for 2 hours. Activated natural zeolite was prepared using NaOH concentrations of 4, 6, and 8 M for 1.5 hours, then characterization was conducted through atomic absorption spectroscopy (AAS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), gas sorption analysis (GSA), and scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX). The results showed that AAS had a potassium content of 7.175 mg g-1 in 100 mL and 358.785 mg g-1 in 500 mL of snake fruit peel. FTIR analysis showed the presence of O–H and Si–O functional groups, while sharp XRD peaks were consistent with the JCPDS data. GSA characterization identified the optimal zeolite concentration as 6 M, and SEM-EDX confirmed the presence of essential NPK elements. The NPK-Biochar-Zeolite SRF fertilizer was found to contain nitrogen (1786.40 ppm), phosphorus (3151.67 ppm), and potassium (15.06 me%), showing superior potassium retention compared to other nutrients. In terms of plant growth, the NPK-Biochar-Zeolite SRF significantly increased water spinach, locally known as “kangkung†in Indonesian, plant height by 2.2% and leaf width by 0.3% compared to other treatments. These results suggest that biochar from snake fruit peel, in combination with activated zeolite, can enhance fertilizer efficiency and support optimal plant growth for sustainable agricultural practices.
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