Effect of Nitrogen, Phosphorus, and Potassium fertilizers on cocoa in Indonesia

Cocoa (Theobroma cacao L.) is one of Indonesia's primary cash crops, supporting an estimated 900,000 households across the country. Smallholder farmers produce most of the crop, but their yields are about 50% of the potential yield. Fertilizer is known to increase cocoa yield. However, yield response to fertilizer application varies depending on the environmental conditions and management practices. There is limited information on the fertilizer requirements of mature cocoa genotypes commonly used in Indonesia. Therefore, an experiment on nitrogen, phosphorus, and potassium applications to hybrid cocoa trees was performed in Banyuwangi, East Java, Indonesia. Cocoa trees were planted on brown sandy podzolic soil. Coconut trees were used as a permanent shade with a density of 37 trees per hectare. The trial involved three N levels: 0, 93, and 186 kg/hectare/year; three P levels: 0, 80, and 160 kg/hectare/year and two K levels: 0 and 61 kg/hectare/year. Treatments were arranged in a factorial randomized block design with 3 replications. Fertilizer applications started 3 years after planting and were repeated every year. From year 3 to 22 after planting, the annual number of pods produced was counted and used to estimate dry bean yield per hectare. From 14 to 22 years after planting, a significant effect of the nitrogen application was observed on cocoa yield. Nitrogen fertilizer applied at 93 and 186 kg/hectare/year significantly increased dry bean yield per hectare by 16.8% and 17.1%, respectively, relative to control. However, there was no significant difference between both nitrogen fertilizer applications in their effect on yield. Although phosphorus and potassium fertilizers had been applied for 19 consecutive years, there was no response to these fertilizers over nine years of data, suggesting high phosphorus and potassium availability in the soil. The data suggest that hybrid cocoa planted on this typical brown sandy podzolic soil in Indonesia only requires nitrogen to sustain high productivity. Phosphorus and potassium fertilizers application are not required for cocoa trees planted on this typical soil type that return the pod husks to the plantation after harvesting. 

Keywords: dry bean yield, NPK fertilizer, leaf N uptake, soil P and K availability