Revitalization of Ultisol Using Biochar from Cassava Harvest Waste Combined with Organic Fertilizer

This study aimed to evaluate the effects of biochar produced from fresh cassava stem and trunk waste, as well as the application of manure, on soil fertility and cassava yield in Ultisols. A factorial randomized block design with three replications was used, testing 4 biochar rates (0, 5, 10, and 15 t/ha) and 3 manure treatments (no manure, cattle manure at 10 t/ha, and chicken manure at 10 t/ha). The initial properties of the Ultisol were characterized by acidity (pH 4.58), low organic carbon (1.80%), total nitrogen (0.12%), total phosphorus (209.90 ppm), exchangeable potassium (0.27 cmol(+)/kg), and cation exchange capacity (4.47 cmol(+)/kg). Application of biochar at the highest rate increased soil pH to 5.5, organic carbon to 2.07%, and cation exchange capacity to 9.82 cmol(+)/kg. There was no significant interaction between biochar and manure treatments for cassava growth and yield, indicating that their effects were independent. Both biochar and manure applications improved plant growth and yield, with the highest yield (124.93 kg/plot) obtained from the combination of 15 t/ha biochar and chicken manure, representing a 13.36% increase over the control (110.20 kg/plot). The combination of the highest biochar rate and chicken manure produced the greatest tuber weight (2.63 kg/plant) and shoot biomass (3.85 kg/plant). The tallest plants (284.60 cm at 8 months) and largest stem diameter (2.70 cm) were observed with the highest biochar rate. Chicken manure consistently improved plant growth across all treatments, with the greatest effects observed at the highest biochar rate. The results indicate that both biochar derived from cassava waste and manure are effective in improving Ultisol fertility and cassava productivity, with the greatest improvements achieved when both amendments are applied together. These findings highlight the importance of targeted nutrient input combinations to enhance crop yield in acidic soils.