Water Hyacinth Biochar: A Sustainable Approach for Enhancing Soil Resistance to Acidification Stress and Nutrient Dynamics in an Acidic Nitisol of the Northwest Highlands of Ethiopia

Soil acidity impacted over 43% of Ethiopia’s arable land and debilitated agricultural productivity. Due to reacidification susceptibility, high costs, and inadequate availability of lime, biochar has emerged as an alternative soil acidity ameliorator. However, biochar application, particularly from invasive plants such as water hyacinth, as a soil acidity amendment and waste management strategy has not fully expanded in Ethiopia. Therefore, this study investigated the potential of water hyacinth biochar (WHB) to enhance soil resistance to acidification stresses and nutrient dynamics in an acidic Nitisol of the northwest highlands of Ethiopia. An incubation study was conducted using nine treatments viz. control (soil only), biochar produced using a furnace (WHBf), and a grounding method (WHBg) each at 1% and 2% application rates, lime (L), fertilizer (F), 2% WHBf combined with fertilizer (2WHBfF), and lime combined with fertilizer (LF). Soil samples, except the control, underwent simulated acidification with HNO3. The results showed that WHB decelerated nitrification, reduced H+ ions released into the soil, and enhanced available phosphorus and nitrogen dynamics. After incubation, 1% and 2% WHB applications increased soil pH in the range of 0.30–0.35 and 0.72–0.86 units, respectively, compared to the limed soil. Conversely, exchangeable acidity decreased by 26.5% to 28.8% and 58.4% to 63%, respectively. The 2WHBfF treatment led to soil pH increases of 0.71 and 0.90 units, with exchangeable acidity reductions of 49.8% and 64.7% compared to the LF and F treatments, respectively. Compared to lime, WHB treatments demonstrated more effective resistance against soil acidification from nitrification and simulated acidification with HNO3. Therefore, WHB can be used as a sustainable approach to increase soil resistance against various acidification stresses while aiding in soil nutrient management. The study’s findings can offer valuable insights to change environmental challenges into sustainable soil acidity management approaches.