Wara Dyah Pita Rengga, Ratna Dewi Kusumaningtyas, Haniif Prasetiawan, Suphacai Amkha
The intensive use of urea fertilizer in agriculture still suffers from low nitrogen use efficiency due to nutrient loss through volatilization and leaching. This condition reduces crop productivity and causes adverse environmental impacts. One promising approach is the development of slow-release fertilizers (SRF) utilizing biochar as a nutrient carrier. This study explores a greener alternative by combining physically and chemically activated rice husk biochar with three natural binders— starch, molasses, and soybean seed coat powder—to engineer SRF-coated urea granules from locally available biomass. Coating thicknesses of 487 μm (starch), 387 μm (molasses), and 370 μm (soybean seed coat) were achieved, with FTIR analysis revealing distinct bonding mechanisms: starch formed robust hydrogen bonds and mechanical interlocking with notable swelling capacity, molasses contributed tacky hydrogen bonding and van der Waals interactions, and soybean seed coat established stronger interfacial NH–CO and Si–O–C chemical linkages. Performance testing demonstrated that chemically activated biochar paired with starch delivered the most effective barrier, achieving the highest water retention (91.1%) and the lowest nitrogen release (8%), while molasses showed intermediate results and soybean seed coat—despite superior bonding—was limited by its thinner layer. These findings establish that waste-derived, bio-based SRF coatings can meaningfully reduce nitrogen loss, improve fertilizer efficiency, and support a transition toward environmentally sustainable and food-secure agriculture. © The Author(s) 2026.
Chemical Engineering Program Study, Faculty of Engineering, Universitas Negeri Semarang, Jawa Tengah, Kota Semarang, 50229, Indonesia; Department of Soil Science, Faculty of Agriculture, Kasetsart University, Nakhon Pathom, Kamphaeng Saen, 73140, Thailand
