ABSTRACT
The need to fertilise cacao (Theobroma cacao L.) emerged at the very beginning of the establishment of high-yielding commercial cacao plantations. Results of fertiliser trials were first published in a study conducted in Cameroon in 1910, quickly followed by Java, Trinidad and Ghana, among others (Verlière, 1981). The objective of these studies was to evaluate the effect of each nutrient supplied separately on cocoa yields. The results showed that phosphorus (P) and potassium (K) have always had positive effects on cacao yields. Although calcium (Ca) and magnesium (Mg) have also had positive effects on yields, the responses were much more variable and the quantities were dependent on the environmental condition. The variability of yield responses to nutrients pointed to the need to link the nutrients with each other or with other factors, in particular with soil, climate and topography. In the case of nitrogen (N), a significant effect on yields was rarely observed, except when the intensity of shading is reduced (Evans and Murray, 1953). There are three reasons for the contrasting effects of N (positive, neutral or negative) and its relationship to shading.
