Comparison of leaf mineral content and soil nutrient status and their combined effect as predictors of cocoa (<i>Theobroma cacao</i> L.) bean yield

Abstract

There is a dearth of research focusing on predicting cocoa bean yield using soil nutrients and/or leaf mineral content, even though such yield predictions exist for other crops. The study examined the relationship between soil nutrients, cocoa leaf mineral content, and yield. A progeny trial field in Bunso with two cocoa varieties and thirty stands was selected from three plots. Sixty pairs of soil samples were taken from the surface and subsurface within a two-meter rhizosphere diameter. Four fully expanded young leaves were sampled from each selected tree three times during the season. Both the soils and leaves were analyzed for nutrient content. The results indicated low correlation coefficients between the soil and the leaf nutrients. The separate multiple regression of the nutrient content of surface soils against pod number, the subsurface soil nutrients against the pod number, and the leaf nutrient against the pod number all recorded low significance (p < 0.05) R² (0.32, 0.36, and 0.20, respectively). However, when soil nutrients at each depth were combined separately with leaf nutrients and regressed against the pod number, relatively greater R² values were recorded (0.61 and 0.57, respectively). The combined soil and leaf nutrient content at each depth was a better predictor of yield than using them separately. Soil nutrients were found to have a better relationship with yield than their leaf counterparts. It was also found that the ideal time for soil and/or leaf sampling is at the onset of the rainfall.