International Journal of Plant & Soil Science

Acid sulphate soils of Kerala are characterized by extreme acidity and toxic concentrations of aluminium (Al³⁺) and iron (Fe²⁺/Fe³⁺), which severely restrict crop growth and productivity. A laboratory incubation was undertaken to evaluate the efficiency of organopolymer and silicate-based lime formulations in ameliorating soil acidity and reducing Al and Fe toxicity in acid sulphate soils. The lime formulation comprising of different lime sources (burnt lime, calcium carbonate, dolomite, and phosphogypsum) combined with organic polymers (fulvic acid, polymaleic acid, and polyfumaric acid) and silicate mixture were applied to acid sulphate soil incubated for 90 days under submerged condition. Changes in soil pH (water and CaCl₂), exchangeable acidity, and exchangeable H⁺ and Al³⁺ were determined at 15 day intervals up to 90 days. Results revealed a significant improvement in soil reaction across all lime formulation–treated soils compared to the control. Among the treatments, burnt lime + fulvic acid + silicate mixture (T1) recorded the highest pH in both water and CaCl₂ extracts, indicating rapid and sustained neutralization of acidity. This was further supported by a marked reduction in exchangeable acidity from 2.23 to 1.80 meq 100 g⁻¹, exchangeable Al³⁺ from 1.62 to 1.35 meq 100 g⁻¹, and exchangeable H⁺ from 0.62 to 0.29 meq 100 g⁻¹, accompanied by an increase in pH (H₂O) from 4.71 to 5.30 and pH (CaCl₂) from 4.36 to 4.97 between the 15th and 90th day of incubation, confirming the effective amelioration of both active and potential acidity. The synergistic effect of fulvic acid and silicate mixture enhanced lime reactivity through complexation, chelation, and hydroxyl ion release, facilitating prolonged pH stabilization.