Bridging Local Knowledge and Empirical Science: Validating Farmer Soil Fertility Perceptions Against Laboratory Derived Topsoil Physico-Chemical Properties

Abstract Abstract Smallholder farmers in Sub-Saharan Africa rely heavily on local knowledge systems to assess soil quality and guide land management decisions. However, the extent to which subjective farmer perceptions align with empirical laboratory diagnostics under intensified forage production remains insufficiently quantified. This study evaluated the relationship between smallholder farmers' subjective soil fertility perception tiers (Low: 0–3, Moderate: 4–6, High: 7–10) and laboratory-determined topsoil physical and chemical properties across smallholder dairy-forage production systems in Southwestern Uganda (N = 54). Soil samples collected across Mbarara, Isingiro, Kazo, and Kiruhura districts were analyzed for pH, Organic Matter (OM), Total Nitrogen (N), Available Phosphorus (P), Exchangeable Cations (K + , Ca 2+ , Na + ), Soil texture (Sand, Silt, Clay %), and Bulk Density. Differences across perception tiers were evaluated using One-Way ANOVA and Kruskal-Wallis tests, while Multiple Discriminant Analysis (MDA) and Ordinal Logistic Regression (OLR) were applied to identify the primary physical and chemical drivers of local score groupings. Soil reaction (pH) emerged as the single strongest statistical discriminator of farmer score tiers (Discriminant Coefficient = -0.814, Wald chi 2 = 14.22, p < 0.001), with high-scoring fields clustering within an optimal slightly acidic range (pH 5.69 ± 0.49) and low-scoring fields exhibiting near-neutral to alkaline conditions (pH 7.10 ± 0.26). Clay percentage served as the primary physical driver (p = 0.009), with high-fertility tiers possessing significantly higher clay fractions (28.88% ± 7.66%) than low-fertility tiers (19.00% ± 2.65%). Conversely, essential macronutrients—including Organic Matter (p = 0.199), Available Phosphorus (p = 0.348), and Exchangeable Potassium (p = 0.271)—did not significantly differentiate farmer perception groupings. Smallholder soil quality perceptions in Southwestern Uganda are primarily calibrated to observable physical attributes (clay urea, water retention) and pH-mediated plant stress, creating a diagnostic blind spot for sub-surface macronutrient depletion. Sustainable forage intensification in the Cattle Corridor requires hybrid diagnostic frameworks that pair farmer local knowledge with routine laboratory chemical soil testing.