Resource Circularity in Oil Palm–Cattle Integrated Systems: A Scenario-Based Assessment of Material Flows and Nitrogen Cycling Toward a Circular Bioeconomy

Oil palm plantations generate substantial biomass and by-products with potential to support the circular bioeconomy and crop–livestock integration. This study assessed biomass and nitrogen flows across three oil palm–cattle integration scenarios using material-flow analysis and nitrogen flow diagrams. Field observations were conducted in April 2026 in a seven-paddock grazing area. Scenarios A and B reflected existing conditions, whereas Scenario C represented a potential model incorporating assumed by-product utilization pathways. Cattle grazing was associated with an estimated 43.2% reduction in understory biomass relative to the non-integrated oil palm plantation. Under the assumed pathways, Scenario C indicated greater material-flow connectivity and nitrogen recycling, with the highest total N input, recycled N, and N recycling rate at 241 kg N/ha/year, 54.5 kg N/ha/year and 22.6%, respectively, while reducing unused oil palm by-products through palm kernel meal utilization. External N input remained 180 kg N/ha/year across scenarios, while product N output increased from 67.2 kg N/ha/year in Scenario A to 71.1 kg N/ha/year in Scenario C. Overall, cattle integration increased biomass utilization and internal nitrogen recirculation, although substantial N surpluses, estimated N2O-related emissions, and unutilized residues remained. These findings indicate opportunities to improve nutrient recovery and by-product utilization without implying reduced dependence on external fertilizer inputs.