Agro -Waste Substrates for Agaricus bisporus Cultivation in a Tropical Environment: Cocoa Pod Husk–Rice Bran Blends as Low-Cost Alternatives to Phase II Compost

The adaptation of Agaricus bisporus (J.E. Lange) Imbach cultivation to tropical environments using locally available agro-wastes represents a significant unmet challenge in African food biotechnology. This study evaluated seven substrate treatments — cocoa pod husk (CPH) alone (T1), sawdust alone (T2, negative control), rice bran alone (T3), CPH–rice bran (3:1 w/w; T4), CPH–sawdust (2:1 w/w; T5), optimised Phase I + Phase II compost (T6, positive control) and commercial Phase II compost (T7, positive control) — under carefully temperature-managed tropical conditions (22–25°C achieved via evaporative cooling, n = 6 per treatment). A sterilised peat–CaCO₃ casing layer (3:1 v/v, 3–4 cm depth, pH 7.4–7.6) was applied 2–3 days after spawn-run completion to stimulate pinhead formation. Biological efficiency (BE), total yield across three successive flushes, spawn-run duration, proximate composition (crude protein, fat, ash, fibre), mineral content (K, P, Mg, Fe, Zn; for T1–T5 only), and contamination incidence were recorded. T4 achieved the highest BE among agro-waste treatments (89.3 ± 5.1%), statistically comparable to T6 (91.2 ± 4.8%) and T7 (95.0 ± 3.2%; Tukey HSD, p > 0.05), while T2 produced the lowest BE (42.1 ± 3.1%). Total yield for T4 was 15.3 ± 1.2 kg m⁻², versus 17.0 ± 0.8 kg m⁻² for T7. Crude protein in T4 fruiting bodies was 33.7 ± 1.4% dry weight (DW), the highest among all treatments and not significantly different from T6 (32.1 ± 1.0%) or T7 (31.5 ± 0.8%; p > 0.05). T4 recorded the lowest contamination rate among agro-waste treatments (3.3%), attributable to its near-optimal C:N ratio of 22:1 and two-stage substrate sterilisation. Mineral concentrations (K, P, Mg) in T4 and T5 fruiting bodies were comparable to published benchmarks for compost-grown A. bisporus; direct comparison to T6/T7 mineral content was not possible as compost control samples were not available for analysis — a limitation explicitly acknowledged. Principal component analysis confirmed clustering of T4 with the compost benchmarks on the productivity axis. These results demonstrate that CPH supplemented with rice bran at 3:1 is a viable, low-energy alternative to Phase II compost for A. bisporus production in tropical regions when adequate temperature management and a properly prepared casing layer are employed.