Valorization of wasted shells into calcium amendments: preparation, characterization, application in acidic soil reclamation and plant nutrition
摘要
Acid sulfate soils severely constrain agricultural productivity due to low pH and high Al3+ toxcity. Conventional limestone-based amendments raise environmental concerns. This study investigates the feasibility of high-reactivity calcium-based amendments derived from waste oyster shells (Ca2+-Oy) and quail eggshels (Ca2+-QE). Waste oyster shells and quail eggshells were calcined at 1000 °C to produce calcium-rich amendments. The admendments were applied to an acid sulfate soil collected from Ben Tre Province, Vietnam, and evaluate the growth response of Ipomoea aquatica, which was monitored over 28 days. Soil pH and plant height were measured, and ANOVA was used to assess statistical differences. Results showed that calcined shell-derived materials rapidly increased soil pH within the first 7 days, effectively alleviating soil acidity and promoting plant growth. Among the tested materials, Ca2+-Oy exhibited the highest Ca2+ content (98.07%) and achieved the most pronounced pH correction, reaching an optimal pH of 5.67 after 7 days. Consequently, Ipomoea aquatica grown in Ca2+-Oy–treated soil attained the highest average plant height (27.3 cm), while the tallest individual plant (33 cm) was observed in the Ca2+-AL treatment. The rapid amelioration effect highlights the superior reactivity of Ca2+-rich shell-derived amendments compared to conventional lime. Overall, this study demonstrates that calcined waste shell-derived calcium materials, particularly Ca2⁺-Oy, offer a promising waste-derived, resource-conserving, high-reactivity amendment for rapid remediation of acid sulfate soils. Their application can enhance early plant establishment and provide a high-reactivity route besides of using traditional non-calcined shells for reducing reliance on mined limestone and support circular economy strategies through food-waste valorization.