Impact of allelochemicals from shade trees bark on the performance of cocoa seedlings

Shade trees are important in cocoa agroforestry systems; however, they release allelochemicals from various parts that affect understory plants. Unfortunately, information on allelochemicals produced by shade tree bark in cocoa plantation remain scarce. This study investigates the effect of allelochemicals from bark of shade trees on cocoa seedlings growth. The experiment was a 4 × 11 factorial study, and the treatments were four different concentrations from each of the 11 tree species. The treatments were laid out in a completely randomized design with four replicates. Data were collected at 30, 60, 90, 120, and 150 days after treatment applications. The tree species alone and bark extract concentrations alone significantly impacted plant height from 90 to 150 days after application. Albizia ferruginea (Guill. & Perr.) Benth, Celtis mildbraedii Engl., and Triplochiton scleroxylon K. Schum produced the highest cocoa seedling heights. All concentrations also influenced stem diameter of cocoa seedlings. Albizia ferruginea enhanced stem diameter significantly among tree species and the control. Tree species and bark extract concentrations interacted to increase fresh root weights and dry plant biomass. Albizia ferruginea consistently increased dry plant biomass, while C. mildbraedii produced the highest enhancement for fresh roots. All concentrations enhanced plant biomass, with the 75 mg mL⁻¹ concentration consistently producing the highest plant fresh and dry weights. Albizia ferruginea and C. mildbraedii can be potential tree species in the cocoa agroforestry when 2-month-old cocoa seedlings are to be transplanted on the field. Bark extract of 75 mg mL⁻¹ concentration can be used as a growth stimulant on cocoa seedlings.