Effect of Organic and Inorganic Amendments on Cd Concentration in Cacao (Theobroma cacao) Seedlings

Aims: Cacao is a highly profitable tropical crop; however, regulations may affect its commercialization worldwide. The aim of this study was to assess the effect of inorganic and organic amendments on soil chemical attributes, the biometric characteristics of cacao seedlings grown in cadmium (Cd)-contaminated pots, and nutrient uptake and interactions in the plant. Methods: The experiment was carried out under greenhouse conditions using dolomite, calcium hydroxide, triple superphosphate (TSP), diammonium phosphate (DAP), potash (KCl), potassium sulfate (K2SO4), cacao pod compost, poultry manure, and seabird guano. The experiment lasted four months, during which soil properties (pH, P, Ca, Mg, K, organic matter, available Cd), biometric characteristics (height, diameter, number of leaves, dry weight), nutrients (P, Mg, K, Cu, Fe, Mn and Zn), and Cd concentration (shoots and roots) were measured. Results: Calcium hydroxide, TSP + KCl and cacao compost were the best treatments for improving soil fertility, reducing available Cd, and improving seedling growth. Plant dry weight was higher with DAP + KCl. Regarding macro- and micronutrient uptake, calcium hydroxide, DAP + KCl and poultry manure enhanced nutrient uptake in cacao under Cd stress. Shoot Cd concentration was reduced by Ca(OH)2 and all the organic amendments, with cacao compost being the most effective. Conversely, inorganic fertilizers increased Cd concentrations compared with the control. Conclusions: Cacao compost with TSP and Ca(OH)2 reduced shoot Cd by nearly 55% compared with the control. These results are promising; however, field validation and direct measurement of bean Cd are still required.