INFLUENCES OF SHADING AND FERTILIZATION ON ON-FARM YIELDS OF COCOA IN GHANA

Richard Asare,Bo Markussen,Anders Ræbild,Rebecca Ashley Asare,Winston Adams Asante

doi:10.1017/s0014479716000466

Abstract

SUMMARYMost cocoa farms in Ghana are cultivated in complex agroforest systems, with plant growth and cocoa productivity being affected. The objective of this study was to investigate how shade trees affect cocoa yield, temperature and soil nutrients in low-input cocoa systems. Establishing plots on 24 farms in four locations (districts) in Ghana, we assessed the influence of varying canopy cover and fertilization on cocoa yields. Results showed no relationship between canopy cover and cocoa yields in the light crop season (February to August). For the main crop season (September to January), there was an interaction between shade and yields: Yields were higher on no-shade plots than on shaded plots in two districts, whilst there were no differences at the two other districts possibly due to differences in precipitation and soil nutrient status. On the other hand, there was a positive effect of increased canopy cover on yields within the shaded plots. Soil nutrient analyses revealed no significant differences between shaded and no-shade plots and adequate levels of N, K+, Fe2+, Cu2+ and Zn2+ were recorded. However, soil contents of P, C, Mg2+ and Ca2+ were below recommended values. Peak temperatures recorded in the cocoa canopies were above the recommended range for this species. Although shade trees had a slight modifying effect on peak temperatures, the magnitude appeared too small to have any practical effects.

Highlights

SUMMA RY Most cocoa farms in Ghana are cultivated in complex agroforest systems, with plant growth and cocoa productivity being affected
For the main crop season (September to January), there was an interaction between shade and yields: Yields were higher on no-shade plots than on shaded plots in two districts, whilst there were no differences at the two other districts possibly due to differences in precipitation and soil nutrient status
It should be acknowledged that shade trees differ widely in the canopy cover (CC) that they provide (Asare and Ræbild, 2016) meaning that some species may have larger effects on air temperatures than others. These on-farm experiments showed that increased CC of shade tree had a positive effect on cocoa yield in some locations and a negative effect in other ones

Summary

Introduction

SUMMA RY Most cocoa farms in Ghana are cultivated in complex agroforest systems, with plant growth and cocoa productivity being affected. In Ghana, traditional or extensively managed smallholder plantations are established by sowing cocoa seeds and/or planting seedlings at random on completely cleared forest (primary or secondary) or fallow lands Results of long-term trials on relationship between shade, fertilizer application and yield conducted in a forest environment in Ghana showed very high yields after shade removal in well-established cocoa plantations on fertilized soils (Ahenkorah et al 1974; 1987; Cunningham and Arnold, 1962). Whilst eliminating shade may boost yield in the short term, a non-shaded cocoa system is not necessarily economically justified considering the negative effects associated with the lack of shade and the increased demand for agro-chemical inputs in order to maintain productivity. Ahenkorah and company attributed this to high K buffering capacity of most soils in Ghana

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