Biochar-Amended Polluted Soil for Rhizophora racemosa Growth

Background and Objective: Soil physico-chemical properties play critical role in determining soil fertility, structure, and its ability to support plant growth. However, these properties are often negatively altered by anthropogenic activities, particularly hydrocarbon pollution from spent engine oil, which leads to soil degradation and reduced productivity. This study assessed the effect of biochar on the physicochemical composition of soil polluted with spent engine oil used in growing Rhizophora racemosa.Materials and Methods: A randomized complete block design was used with four treatments: garden soil (GS), garden soil plus biochar (GSB), garden soil plus 6% spent engine oil (GSSEO), and garden soil amended with both biochar and engine oil (GSBSEO), each treatment was replicated three times. Pre- and post-planting soil samples were analyzed for total organic matter (TOM), total organic carbon (TOC), total hydrocarbon content (THC), soil moisture content, and pH. Data were analyzed by ANOVA, and significant means separated using LSD at 5% probability. Results: The biochar application significantly enhanced TOM (20.70%) and TOC (12.00%), while spent engine oil reduced these values and increased THC. The combined treatment (GSBSEO) demonstrated that biochar could partly reduce the negative effects of oil contamination. Moisture content was highest in the biochar-treated soil (24.63%), confirming biochar’s role in enhancing water retention. Soil pH remained relatively neutral across treatments, with no statistically significant changes observed. Conclusion: The potential of biochar as a sustainable amendment for improving soil quality and mitigating the adverse effects of hydrocarbon pollution. These findings provide valuable insights for the rehabilitation of degraded coastal soils and support the restoration of ecologically important mangrove species such as R. racemosa.