Sustainable cocoa intensification: evaluating biochar placement methods and MKP application rate on yield in degraded tropical soils

Abstract

Abstract Cocoa productivity in degraded tropical soils is frequently constrained by low nutrient retention, high leaching losses, and poor soil structural stability, particularly in highly weathered acidic soils. In smallholder cocoa systems, the limited use of soil amendments such as biochar further reduces nutrient use efficiency and crop performance. This study evaluated the effects and interactions of cocoa pod husk biochar placement techniques and mono potassium phosphate (MKP) application rates on the physiological characteristics and productivity of 10-year-old cocoa trees in a smallholder plantation in East Kalimantan, Indonesia. A split-plot design was employed, with three biochar placement methods (ring placement, biopore insertion, and surface broadcasting) assigned to the main plots and four MKP rates (0, 10, 20, and 30 g tree−1) to the subplots. Biochar placement significantly influenced stomatal density, whereas MKP application rate significantly affected most reproductive and yield-related traits. Significant interaction effects between biochar placement and MKP rate were observed for the number of flower clusters, yield per tree, and yield per hectare. Orthogonal polynomial analysis revealed predominantly quadratic dose-response relationships, indicating the existence of optimal MKP rates under each biochar placement method. Surface broadcasting consistently produced the strongest yield response, with coefficients of determination reaching R2 = 0.95. Correlation analysis showed that yield per hectare was strongly associated with the number of harvested pods and yield per tree, whereas 100-seed weight and stomatal density were not significantly correlated with final productivity. These findings suggest that yield improvement in cocoa is primarily driven by enhanced fruit retention rather than seed size. Overall, the integration of strategically applied cocoa pod husk biochar with optimized MKP fertilization represents a promising strategy to improve nutrient use efficiency and productivity in smallholder cocoa systems.

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