Purpose <p>Low fertilizer application due to sky-kissing costs and short-term effects of lime could not alleviate soil acidity and crop productivity depletions in Ethiopian highlands. Biochar, a promising soil conditioner, can alleviate this problem. This study examined the impacts of water hyacinth biochar (B) integrated with organic and synthetic fertilizers on soil properties, nutrient leaching, and plant growth.</p> Methods <p>A pot experiment was conducted on barley using 11 treatments: control (soil only), recommended rate of nitrogen fertilizer (69&#xa0;kg&#xa0;ha^–1; F), lime plus fertilizer (LF), poultry manure at 50% (50PM) and 100% (100PM) of recommended rate of&#xa0;nitrogen, and factorial&#xa0;combinations of 1% B (1B) and 2% B (2B) with F, 50PM, and 100PM (1BF, 1B50PM, 1B100PM, 2BF, 2B50PM, and 2B100PM, respectively).</p> Results <p>B–PM combinations outperformed B–F, significantly increasing soil pH by 0.79–1.65 units, organic carbon by 50.8–122%, and available phosphorus by 205–507%, while reducing exchangeable acidity by 80.6–97.9%. 2B100PM, 2B50PM, and 2BF treatments entirely eliminated exchangeable aluminum. B–PM and B–F treatments decreased ammonium leaching by up to 99.2% and 97.8%, and nitrate leaching by up to 97.5% and 95.6%, respectively. Shoot and root biomass increased in the order: control &lt; 50PM &lt; F &lt; LF &lt; 100PM &lt; 1B50PM &lt; 1BF &lt; 1B100PM &lt; 2B50PM &lt; 2BF &lt; 2B100PM.</p> Conclusion <p>Integrating water hyacinth biochar with organic and synthetic fertilizers can be a novel avenue in alleviating soil acidity, reducing nutrient leaching, and enhancing plant growth while offering sustainable weed management and mitigating environmental pollution.</p> Graphical Abstract <p></p>