The Influence of Shade and Organic Fertilizer Treatments on the Physiology and Establishment of Theobroma cacao Clones

K Acheampong,P Adu-Yeboah,A Daymond,P Hadley

doi:10.9734/ajea/2015/15206

Abstract

Aims: This experiment aimed to determine whether the soil application of organic fertilizers can help the establishment of cacao and whether shade alters its response to fertilizers. Study Design: The 1.6 ha experiment was conducted over a period of one crop year (between April 2007 and March 2008) at the Cocoa Research Institute of Ghana. It involved four cacao genotypes (T 79/501, PA 150, P 30 [POS] and SCA 6), three shade levels (‘light’, ‘medium’ and ‘heavy’) and two fertilizer treatments (‘no fertilizer’, and ‘140 kg/ha of cacao pod husk ash (CPHA) plus poultry manure at 1,800 kg/ha). The experiment was designed as a split-plot with the cacao genotypes as the main plot factor and shade x fertilizer combinations as the sub-plots. Methodology: Gliricidia sepium and plantains (Musa sapientum) were planted in different arrangements to create the three temporary shade regimes for the cacao. Data were collected on temperature and relative humidity of the shade environments, initial soil nutrients, soil moisture, leaf N, P and K+ contents, survival, photo synthesis and growth of test plants. Results: The genotypes P 30 [POS] and SCA 6 showed lower stomatal conductance under non-limiting conditions. In the rainy seasons, plants under light shade had the highest CO2 assimilation rates. However, in the dry season, plants under increased shade recorded greater photosynthetic rates (P = .03). A significant shade x fertilizer interaction (P = .001) on photosynthesis in the dry season showed that heavier shade increases the benefits that young cacao gets from fertilizer application in that season. Conversely, shade should be reduced during the wet seasons to minimize light limitation to assimilation. Conclusion: Under ideal weather conditions young cacao exhibits genetic variability on stomatal conductance. Also, to optimize plant response to fertilizer application shade must be adjusted taking the prevailing weather condition into account.

Highlights

Cacao is cultivated through the humid tropics with over 70% of cocoa being produced in West Africa [1]
The lower shade levels for the shade regimes were obtained in the dry season as the shade plants experienced more rapid leaf senescence and leaf shedding
The influence of overhead shade in this study on photosynthesis differed between seasons

Summary

Introduction

Cacao is cultivated through the humid tropics with over 70% of cocoa being produced in West Africa [1]. In order to meet the increasing demand for cocoa [2], it will increasingly be necessary for farmers to selectively replant their cocoa farms thereby replacing aging stock with more productive varieties. Re-planting of cacao farms in West Africa can be challenging where there is scanty overhead shade [3,4]. There is a need to replenish the ‘mined’ soil nutrients in order to sustain cocoa production. Because of health and environmental concerns there has been a steady growth in the demand for organically produced cocoa in recent times [12,13]. It is worthwhile to investigate whether organic fertilizers aid in re-establishing cacao on soils with a previous history of cacao cultivation. Since the use of overhead shade has been shown to aid seedling survival [14] the interaction between fertilizer addition and overhead shade was studied

Results

Discussion

Conclusion