Microbial Composting of Cacao Residues Improves Compost Quality and Cacao Seedling Morphophysiology

Abstract

Article HistoryStable, nutrient-enriched organic growing media are essential for producing vigorous cacao seedlings, particularly in smallholder nurseries.Cacao plantation residues, especially cocoa pod husks, are potential compost feedstocks but require controlled microbial decomposition to improve their agronomic value.However, comparative evidence linking biodecomposerinduced changes in cacao-residue compost quality with the morphological and physiological responses of cacao seedlings remains limited.This study evaluated the effects of cacao plantation residue compost produced using local microorganism solution (MOL), Trichoderma harzianum, Pleurotus ostreatus, and their combinations on compost chemical quality and the growth and physiological responses of cacao (Theobroma cacao L.) seedlings.The experiment used a randomized complete block design with ten treatment packages and three replications.Compost feedstock consisted of cocoa pod husk, Gliricidia sepium leaves, and banana pseudostem at a fresh-weight ratio of 70:10:20.Variables included compost chemical properties, seedling growth, stomatal traits, chlorophyll content index, and leaf optical properties at 14 weeks after treatment.Biodecomposer-treated compost increased organic C, total N, available P, available K, and cation exchange capacity, while reducing the C/N ratio compared with compost without biodecomposer.These changes improved plant height, leaf number, leaf area, stem diameter, and root length.MOL at 40 mL L⁻¹ was the most effective treatment for improving compost nutrient status, seedling growth, and stomatal traits.Compared with compost without biodecomposer, this treatment increased total N by 44.9%, cation exchange capacity by 50.3%, plant height by 52.3%, leaf area by 250.8%, stem diameter by 57.6%, and root length by 58.9%.In contrast, the combined application of MOL, T. harzianum, and P. ostreatus had stronger effects on organic C, chlorophyll content index, and leaf absorptance.These findings show that cacao plantation residues can be converted into functional microbial compost to improve nursery media quality and support sustainable cacao seedling production.Under the tested screenhouse conditions, compost produced with MOL at 40 mL L⁻¹ and mixed with Ultisol at a ratio of 1:2 (w/w) was the most effective tested nursery-medium component for producing vigorous cacao seedlings.

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