The effect of fertilization on leaf nutrient content distribution of the cocoa tree and the relation to the leaf mass area (LMA)

Abstract
The cocoa tree (Theobroma cacao) needs nutrients for plant growth and to develop cocoa fruits. Yield reduction can take place due to limiting nutrients. Fertilization can, if used in the right way, reduce the nutrient limitation. Leaf nutrient analysis can be used to obtain fertilizer requirements. But the high tree variability between cocoa trees can obstruct analysis, which increases the need of a standardized measurement. The observed leaf nutrient concentrations demonstrate little influence of fertilization, which is probably because of tree variability. Only the measured P-concentrations do show an influence of fertilisation. This experiment confirms that the use of sun or shade leaves affects nutrient measurements, shade leaves have higher K- and P-concentrations. But there are no significant differences for N-, Ca- and Mg-concentrations, possibly because of tree variation as well, so the influence cannot be predicted for these nutrients. The experiment is used to show if the LMA (Leaf Mass per Area) can be used to standardize from which layer of the canopy leaf samples for nutrient analysis have to be harvested and to see if either leaf samples with a high LMA (sun leaves) or low LMA (shade leaves) will show a higher effect of fertilization. As expected LMA is higher in sun than in shade leaves, and the experiment shows that there could be some preference for sun leaves because there is no difference in LMA between 2018 and 2019 while there is for shade leaves. The LMA experiences no overall influence of pruning. LMA could be correlated to leaf nutrient content, but the relations are weak so the comparison is not really reliable. This thesis agrees with other research that it is really hard to standardize leaf nutrient analysis.