Biomass and nutrient distribution in cocoa (Theobroma cacao): a case study in Ivory Coast.

Abstract
The mineral nutrition of cacao agro-ecosystems is a key factors for achieving potential yields. Therefore, there is a need to quantify and understand the total cacao tree nutrient requirements. This study was carried out in coordination with CNRA (Centre National de Recherche Agronomique) in Divo, Ivory Coast. We investigated the distribution of biomass and nutrients in cocoa tree components. We harvested and measured a total of 12 cacao trees of four age classes. We found that management practices such as pruning have a great effect on biomass distribution. In fact, the fraction of dry matter allocated to leaves and branches decreased, stem increased, and roots was maintained in relation to total biomass with increasing tree age. In our study, for all tree age classes, the greatest contribution to total biomass was branches > roots > leaves > stem. Also, we developed allometric relations. We found that the best predictor for tree components biomass and total biomass was stem diameter. We noticed, that recyclable plant components have a higher nutrient content, like leaves and pods, whereas less recyclable components like stem, branches and woody roots, a lower content. Also, the order of nutrient concentration is component specific. We found mobilization of N, P and K from older to younger leaves which lead to concentration of Ca and Mg in senescing leaves. Also, the highest amount of N was found in the beans and newly produced leaves, and K in the pods. Leaf position in the canopy had a significant effect on leaf thickness, and SPAD units but did not affected leaf nitrogen content. Based in our findings, the use of a SPAD meter do not stands as a promising option to determine leaf N content on cacao trees. On the other hand, the use of an increment borer arises as an option for wood nutrient estimation. Finally, we determined that the wood density of six branch orders was constant of about 0.41 g/cm3. Our results have implication for modelling purposes relating growth, biomass and nutrient allocation in cacao trees. Currently, our research is the most complete study on biomass and nutrient distribution in cacao trees.