Effects of fertilizer application on cacao pod development, pod nutrient content and yield

Samenvatting

Fertilizer application in cacao production systems in West Africa yields highly variable results, ranging from no effect to doubling of the yield. Mechanisms underlying yield responses to increased nutrient availability are still largely unkown. In this study, we assessed how fertilizer application affects pod development and production of cacao trees in a full sun cocoa system in Côte d'Ivoire and a shaded cocoa system in Ghana. We monitored pod growth over time and the number of pods produced simultaneously on the trees in the minor and major harvest seasons. Furthermore, we measured nutrient concentrations in cherelles and beans and husks of developing pods in the major harvest season to estimate the total nutrients allocated to developing pods per tree. Lastly, we performed detailed yield measurements (number of pods, location in the tree (canopy or trunk), pod size and bean content) in 2020 for the plot in Côte d'Ivoire. Our results showed that, in the major harvest season, pods on fertilized trees grew wider (average: 15.4 cm) than pods on unfertilized trees (average: 11.9 cm). A higher pod growth rate resulted in a larger final pod size; larger pods took longer to mature. In the major harvest season, more cherelles on fertilized trees than on unfertilized trees reached maturity despite having an equal or lower nutrient content. Competition for assimilates rather than nutrients seems to induce cherelle wilt. In pods past wilting stage, fertilizer application slightly influenced nutrient dynamics of developing pods but not the final nutrient content in ripe pods. Lastly, increased nutrient availaibility did not change the absolute number of pods a tree produced annually. However, fertilizer application did increase the estimated annual dry bean yields from 2260 kg ha⁻¹ to 2930 kg ha⁻¹ by increasing the number of pods that developed during the major harvest season, when pods were heavier and the bean weight within the pods was relatively higher.