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Shade tree species with Ca-enriched litter improve cocoa agroforest functions in Central Cameroon

Sauvadet M., Saj S., Freschet G.T., Essobo Nieboukaho J.D., Enock S., Becquer T., Tixier P., Harmand J.M.. 2019. In : Dupraz Christian (ed.), Gosme Marie (ed.), Lawson Gerry (ed.). 4th World Congress on Agroforestry. Book of abstracts.. Montpellier : CIRAD; INRA, p. 738-738. World Congress on Agroforestry. 4, 2019-05-20/2019-05-22, Montpellier (France).

Associating shade trees to cocoa plantations supply many services to farmers, yet their contrasting impacts on soil fertility in relation to their traits remains little understood (Blaser et al., 2017). In 2017, 6 cocoa shading modalities of cocoa were studied across 8 farmers' plots (Bokito district, Cameroon): unshaded, shaded with Canarium schweinfurthii, Dacryoides edulis, Milicia excelsa, Ceiba pentandra and Albizia adianthifolia. For each shading modality, we analyzed the plant association community values of: litterfall; N and P resorption efficiency; litter C, macronutrients and tannins content; Van Soest fractions and litter pH. We measured soil C, N, NO3 -, NH4 +, Olsen P, pH, bioassay and cocoa yield. Shade tree ¿ cocoa association increased total litterfall for all the species without impacting on cocoa yield. Further, litter N was higher with Albizia, while litter P and Ca were higher with Milicia and Ceiba and litter pH was lower with Canarium and Dacryodes. Soil properties were not impacted by Canarium and Dacryodes, while Albizia, Milicia and Ceiba increased soil inorganic N and P content and bioassays (Fig 1). Finally, soil pH and total C and N content increased under Milicia and Ceiba, leading to the highest increase in soil fertility. Multiple regression models suggested a critical role of litter Ca to improve soil fertility in such systems. Using shade trees like Milicia or Ceiba with high Ca cycling should thus be advised to farmers to improve their system.

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