Mitigation of Cadmium Uptake in Theobroma Cacao L: Efficacy of Soil Application Methods of Hydrated Lime and Biochar

Purpose Although mitigation approaches have been developed to reduce Cd in cacao beans, the efficacy of the approaches have been inadequate to make them economically viable. The objective was to determine the application method that would be most efficacious with respect to rapidity of effect, magnitude of reduction and persistency of effect on Cd in cacao. Method A field study was conducted using two soil amendments, hydrated lime and biochar, at recommended rates using three methods of application, soil surface application with incorporation (SA), soil injection (SI) or deep placement using an auger (AA) along with a control. The experiment was arranged in randomized complete block design with three replications with 15 trees per replication. Phytoavailable soil Cd, soil pH, CEC and total leaf Cd concentration were monitored monthly on three guarded trees per plot over a one-year period. Results The efficacy of application of hydrated lime by SI was significantly better than SA in terms of rapidity of the effect on leaf Cd in comparison to the control (40% reduction compared to 30%) as well as its persistency. With biochar, again the SI was significantly better than SA with regards to reducing leaf Cd levels in comparison to the control (35% reduction compared to 20%) but the time taken to action and the persistency were lower compared to hydrated lime application. AA did not significantly reduce Cd level in the leaf with either hydrated lime or biochar application. Conclusion Overall the application of the amendments using SI was much more effective in reducing Cd accumulation in cacao leaves for both amendments.