|Keywords||cacao, cocoa, copper fungicides, earthworm cast production, humid tropics|
|Abstract||The initial results of an experiment to compare the agronomic effects and environmental impacts of different copper fungicide regimes in cacao are presented. Fungicide to control blackpod (Phytophthora megakarya Bras. & Griff) is the main external input used in cacao (Theobroma cacao L.) systems in southern Cameroon. In a recent survey, farmers classified 33 % of their cacao holdings as abandoned. Given increased interest in cacao production it is important to know what yields are possible from previously abandoned fields and what is the yield response to fungicide. An experiment was established in farmers’ cacao farms that had been abandoned for three years. The effects of high and low fungicide applications versus a zero-spray control on cocoa yield and various environmental parameters, including earthworm cast production and earthworm mediated nutrient cycling, were assessed. Fungicide treatments were the recommended application rate (high), 33% of the recommended rate (low) and zero application. Consequent yields of cocoa were 358, 203 and 48 kg dry beans ha-1 in the high, low and zero spray treatments, respectively in the first year after abandonment. Topsoil from cacao plots had higher pH, and higher exch. Mg and Cu concentrations than the forest soil. Regarding trade-offs between ecological sustainability criteria, there was no significant effect of fungicide on earthworms, the major ‘ecosystem engineer’ in the system. However, relative to the forest system, casting levels ranged from 24 to 36% in the cocoa. Copper concentrations of casts were lower than copper concentrations in soil for the cacao plots. This suggests that earthworms are avoiding copper uptake. Casts derived from the high fungicide application plots had a higher percentage of clay than those derived from the low fungicide application and zero-spray treatments. This suggests that the earthworms may be feeding more in the deeper soil layers where the clay content was higher to avoid the soil with higher copper concentrations near the surface. Economic returns and profit would be greater in the high fungicide application treatment at farm gate prices higher than 315 CFA kg-1 (€ 0.48). Prices have generally been higher than this in the past five years. The zero spray treatments produced such low yields, even with rigorous phytosanitary harvests that it cannot be recommended. In conclusion, the manufacturer recommended spraying regime was the most profitable and no significant negative environmental consequences were detected over the time frame of the experiment.|
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