OICC Press International Journal of Recycling of Organic Waste in Agriculture 2251-7715 12 4 2024 03 08 Crab shell biowaste hydroxyapatite as inert material for gradual releaser of crop nutrients for sustainable food production 10.30486/ijrowa.2023.1964772.1518 EN Yusuf Wibisono Department of Bioprocess Engineering, Faculty of Agricultural Technology, Universitas Brawijaya, Malang 65141, Indonesia 0000-0001-8534-1696 Vibi Rafianto Department of Agricultural and Biosystems Engineering, Faculty of Agricultural Technology, Universitas Brawijaya, Malang 65141, Indonesia Dikianur Alvianto Department of Bioprocess Engineering, Faculty of Agricultural Technology, Universitas Brawijaya, Malang 65141, Indonesia Gunomo Djoyowasito Department of Agricultural and Biosystems Engineering, Faculty of Agricultural Technology, Universitas Brawijaya, Malang 65141, Indonesia Bayu Dwi Apri Nugroho Department of Agricultural and Biosystems Engineering, Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta 55281, Indonesia Chusnul Arif Department of Civil and Environmental Engineering, Faculty of Agricultural Technology, IPB University, Bogor 16680, Indonesia Journal Article 2024 03 08 Purpose Aggressive use of crop fertilizer during food production caused an overburden in the environment. Gradual release of crop nutrients from the fertilizer could decrease the massive utilization of fertilizer. The advantages are two folds, cheaper cost, and environmentally friendly crop production.Method Slow-release fertilizer was prepared by encapsulating hydroxyapatite (HA) with a single fertilizer. The HA which derived from crab shell biowaste was synthesized by the wet precipitation method. The nitrogen release test was carried out every 5 minutes for 1 hour using the percolation method, then the percolates were tested for the total nitrogen content. Fertilizer was applied to see its effect on the vegetative and generative growth of tomato plants. Five treatments were applied: without fertilizer as control, ammonium sulfate (AS) fertilizer, hybrid AS-HA fertilizer, urea (U) fertilizer, and U-HA fertilizer.Results AS-HA released nitrogen at 4.45% or three times slower than AS which released 13.51%. U-HA released nitrogen as much as 3.96% or 4.5 times slower than urea which released nitrogen as much as 18.66% in one hour. AS-HA fertilizer provided the best results for overall parameters, with an average height of 102.1 cm for plant height, 7 mm for stem diameter, 82 strands for number of leaves, 4 produced fruits, and 63.5 grams for the fruit weight per plant.Conclusion Slow-release fertilizer with a mixture of hydroxyapatite was able to release nitrogen gradually. Korsmeyer-Peppas model was the best-fitted model for nitrogen release.