Application Strategies
All macronutrients – with the exception of phosphorus and some micronutrients - can be leached.
The majority of cocoa is grown in soils with high phosphorus fixation, meaning higher application rates of phosphorus may be needed. With intensive rainfall, phosphorus can also be lost due to surface run-off.
Nitrogen volatilization is a significant problem and losses of up to 50% of nitrogen applied as urea have been measured. In the tropics, it is assumed that over half of the applied nitrogen and 25% of the potassium and magnesium can be lost. In low CEC tropical soils, 60–85% of the total applied Nitrogen, Potassium, Calcium and Magnesium fertilizer may also be lost. As a result, in order to reduce losses, applications of small, but frequent amounts of fertilizer, should be considered as best practice.
Growers commonly employ regular applications of all fertilizer nutrients during the rainy season with the key use periods being after fruit set and two months before harvest. As a result of the very high nutrient losses that occur, the fertilizer rates required, and commonly used, are much higher than those suggested by theoretical calculation based on removal figures.
Prior to planting, lime should be applied and incorporated in order to help maintain a satisfactory soil pH of above 5.0. During the early immature phase, fertilizer applications have to be more frequent, 3 to 4 times a year, in order to ensure good nutrient supply to the small root system and to minimize nutrient losses. Phosphorus and potassium are particularly important when establishing the cocoa tree.
Mature trees should receive fertilizer at least twice a year; a basal dressing is often given at the beginning of the rainy season. Supplemental nitrogen, calcium and boron should be applied on the basis of field observations to manage the canopy density and to reduce cherelle wilt.
In some countries the fertilizer is buried at application to reduce the risk of nutrient run-off. Once the leaf canopy is complete, the leaf litter is relied on to prevent run-off. Growers can also minimize leaching or run-off losses by using an appropriate rate of fast-dissolving fertilizer that is immediately available to the tree.
Foliar application is used to address an immediate nutritional need or where soil conditions restrict availability of specific nutrients. It can be a highly effective approach in cocoa.
