Soil acidification in cocoa (Theobroma cacao) agrosystems in Côte d'Ivoire: Insights into throughfall and soil solution chemistry responses to soil carbonate amendment

Abstract In former cocoa-producing regions of Côte d’Ivoire, Cocoa ( Theobroma cacao L.) farming exacerbates soil acidification due to prolonged monoculture, nitrogen fertilization and leaching losses, posing a threat to long-term productivity and sustainability. This study evaluated the effectiveness of carbonate amendments (dolomite (CaMg(CO₃)₂) and quick lime (CaO)), in restoring soil chemical fertility across four cocoa plantations on Ferralsols (pH < 5.0). Amendments were applied at rates of 3 t. ha − 1 over three years. Solution collection devices were strategically installed using porous PTFE suction cups at -20 cm and − 40 cm depths in pits for soil solution, and funnel collectors at 1 m above the soil surface for throughfall. Sampling occurred fortnightly during the rainy season and rainfall collected within 24 hours after each rainy event from the second-year post-amendment. Chemical analyses of these solutions included pH, cations (Ca, Mg, K, Na, Fe, Al), and dissolved phosphorus. Results revealed marked soil solution alkalization (pH increase of 1 to 2 units at -20 cm), boosting exchangeable base cations up to 10-fold and phosphorus availability (total soluble P). Throughfall chemistry mirrored these improvements, with nutrient-enriched rainfall (e.g., K⁺ concentrations doubled), highlighting the role of cocoa trees canopy in nutrient recycling and return to the soil. Additionally, dissolved phosphorus is strongly correlated with Al and Fe release in the soil solution, suggesting solubilization of Al-Fe oxide. This approach offers a cost-effective, scalable strategy for mitigating acidification in tropical agroecosystems, enhancing cocoa resilience amid climate variability.