Circular Upcycling of Bauxite Residue (Red Mud) with Cow Manure for Sustainable Forest Restoration: Effects on Neolamarckia cadamba (Roxb.) Bosser Growth in Degraded Mine Soils

Expansion of the global aluminum industry has produced severe landscape degradation through surface bauxite mining and massive accumulation of bauxite residue (red mud). This study explores a circular economy strategy for rehabilitating post-bauxite mining Oxisols in the Tayan Bauxite Mining Cluster (0°02′01″ S, 110°06′07″ E), West Kalimantan, Indonesia, by applying red mud blended with composted cow manure as soil ameliorants. A 6-month field trial using a Randomised Block Design (RBD) (20 plots) assessed the effects of graded red mud–manure combinations on foliar nutrient uptake and vegetative growth of Neolamarckia cadamba (Jabon). Treatment C (1.0 kg red mud + 13.5 kg manure) optimised soil chemical conditions most effectively, yielding the highest foliar macronutrient concentrations per plant (N: 3.47%, P: 0.57%, K: 1.63%) and the greatest height increment (84.99 cm, a 36.9% gain over the unamended control at six months). Higher doses (Treatment D) produced diminishing returns, pointing to an inferred sodium-induced inhibitory threshold based on observed growth responses. These findings indicate that integrating a source of sodium from red mud with organic matter shows strong potential as an effective soil ameliorant for post-mining rehabilitation. The approach supports SDG (Sustainable Development Goals) 12 (Responsible Consumption and Production) by converting industrial waste into a productive soil input, and SDG 15 (Life on Land) by facilitating ecological recovery on degraded mine landscapes.