Soil Physicochemical Parameters and Bibliographically Inferred Microbial Diversity as Drivers of Early-Stage Biodegradation of Colocasia esculenta and Manihot esculenta Starch Bioplastics in Three High-Andean Soils of Ecuador

Single-use plastic residues persist in agricultural and peri-urban soils of the Ecuadorian Andes. Regionally sourced starch-based films are a plausible local replacement for short-lifetime petroleum plastics, yet field-relevant degradation data for tropical high-altitude soils remain scarce. This study evaluated the soil biodegradability of bioplastic films produced from Colocasia esculenta (malanga blanca) and Manihot esculenta (yuca) across three contrasting soils from Chimborazo, Ecuador (ESPOCH, San Andrés and Río Chimborazo; 2825–3249 m a.s.l.) as a function of their physicochemical properties and bibliographically inferred microbial context. The films were prepared by citric acid starch extraction, glycerol plasticization and carboxymethylcellulose reinforcement; the gravimetric weight loss was tracked on days 0, 11, 18, 27, 40 and 47 on n = 20–21 film replicates per soil × feedstock combination, with the soils characterized by their pH, electrical conductivity and organic matter. After 47 days, the malanga films reached 42.3 ± 13.6%, 22.9 ± 10.7% and 54.1 ± 19.3% mean (±standard deviation, SD) weight loss in the ESPOCH, San Andrés and Río Chimborazo soils, respectively; the yuca films reached 24.4 ± 6.5%, 21.1 ± 6.8% and 49.4 ± 18.7%. The between-soil differences were statistically significant at 47 days according to the analysis of variance (ANOVA) (malanga: F = 22.17, p < 0.001; yuca: F = 34.08, p < 0.001; Tukey’s Honestly Significant Difference (HSD)), with the results corroborated by the Kruskal–Wallis method (H = 29.16 and 37.05; both p < 0.001), given the partial departure from normality identified by the Shapiro–Wilk test. The ordering of degradation departed from the bulk organic matter ranking, indicating that microbial community composition, rather than organic matter quantity alone, was the proximal driver. These findings extend the scarce evidence base on cassava/taro film degradation under high-Andean conditions.