Assessing a farmer-based soil classification system vis-à-vis USDA soil taxonomy suborders in Kamuli District, Uganda

Based on 5 years of integrated pedological work in Kamuli District, this study examines how farmers in three villages understand and classify soils. The farmers' knowledge was documented through a participatory approach that included discussions, soil mapping, subsequent field reconnaissance, and 23 pedon descriptions. Based on comparable needs and landscapes, farmers across three villages classified the soils into four groups: Lirugavu, Lubalebale, Mukyanga, and Mutaala. These corresponded to six USDA Soil Taxonomy suborders, Aqualfs, Aquolls, Ustalfs, Ustults, Ustox, and Ustipsamments. Farmers demonstrated spatial awareness through the soil mapping exercise, in which soils were associated with specific landscape positions. A farmer-based ranking in terms of soil productivity aligned with Corn Suitability Rating (CSR2) values, with Lirugavu and Lubalebale as the most and least productive, respectively. The farmer-based soil groupings/ classification distinguished soils by depth of mollic colors, clay content, organic matter (SOM), total nitrogen (N), and cation exchange capacity (CEC). The ability of the soil groupings to discern vertical variation, that is, significant differences from 0–15 cm to 15–30 cm depth layers, was captured only for SOM and N in Lirugavu. Soil Taxonomy suborders captured a wider range of chemical properties and more consistent vertical differentiation. These findings highlight the differences in epistemology but with potential for complementarity between farmer-based and scientific classification systems, leading to integrated approaches to soil assessment and management.