Efficient management of soil micronutrients is crucial for the yield and sustainability of cacao (Theobroma cacao L.), especially in tropical regions. However, specific availability classes for copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn), extracted by Mehlich-1, had not yet been established for the crop in Brazil. This study presents, for the first time, the establishment of these classes, considering two soil layers (0–10 cm and 0–20 cm) in cacao-cultivated areas of southeastern Bahia, Brazil. A comprehensive database, generated by the Renova Cacau project and representative of the main cacao-growing region of the state, was used. Response curves of mean relative yield were fitted as a function of Cu, Fe, Mn, and Zn contents in the two soil layers, applying the boundary line approach. The analysis allowed the classification of these micronutrient availabilities into classes ranging from “very low” to “excessive.” For the 0–20 cm layer, the content intervals associated with the adequate range (mg dm−3) were Cu (1.02–1.52), Fe (33.0–61.0), Mn (9.5–15.8), and Zn (2.1–6.3). These results broaden the scientific basis for soil fertility interpretation in cacao-cultivated soils and support more precise fertilization recommendations, promoting rational micronutrient management and contributing to increased yield and sustainability in cacao cultivation.
