Effect of shade trees in cocoa agroforestry systems on cocoa microclimate and productivity

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The research was conducted to evaluate the effect of shade trees in cocoa systems on the availability of soil moisture, photosynthetically active radiation (PAR), temperature and relative humidity for cocoa in the dry seasons and how these environmental factors influence cocoa productivity. The study was carried out in the Atwima Nwabiagya District (a moist semi-deciduous forest zone) of the Ashanti region of Ghana. Sixteen different shade trees were selected and categorized as low, medium and tall canopy heights. An effect ratio comparing tree sub-canopy effects to the open area effects was adopted and data were analyzed using the R Statistical Package. Soil moisture contents were higher for the medium (0.09) and tall (0.06) canopy height trees but lower for the low canopy heights (-0.07). Morinda lucida (0.19), Spathodea campanulata (0.16) and Ficus capensis (0.13) showed favourable soil moisture effects, however Citrus sinensis (-0.26) revealed lower soil moisture levels in the sub-canopy during the dry seasons. Photosynthetic active radiation was significantly higher for the tall (48.5%) and medium (31%) canopy heights but lower for the low canopy heights (10.7%). Entandrophragma angolense and Terminalia superba had the highest transmitted percentage PAR of 69.2% and 67.1% respectively and the lowest being Mangifera indica (3%). The effect of single standing shade trees in cocoa systems to buffer temperature and relative humidity in the dry seasons were not significant. Cocoa aboveground biomass was higher in the sub-canopies of tall (0.07) and medium (0.01) canopy heights but was however significantly lower for low canopy heights (-0.24). Aboveground biomass was highest in the sub-canopy of Entandrophragma angolense (0.26) but lowest under Mangifera indica (-0.37). The study revealed that potential yields of cocoa were as well higher in the sub-canopies of tall (0.12) and medium (0.06) canopy heights but lower for low (-0.16) canopy height. The pod yields of cocoa were highest under Ficus capensis (0.40) and Ficus exasperata (0.40) but lowest under Terminalia ivorensis (-0.55). Tall and medium canopy height trees in cocoa agroforestry systems potentially ensure higher soil moisture content and PAR availability in the sub-canopy, especially during the dry seasons, which could translate into higher cocoa aboveground biomass and pod yields. The inclusion of low canopy height trees must be done with caution as it may lead to potential yield reduction
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the degree of Master of Philosophy in Agroforestry,
cocoa yields, canopy height, Soil moisture, photosynthetic active radiation, temperature, relative humidity, aboveground biomass