Baseline Physico-Chemical Evaluation and Nutrient Diagnostics of Soils Supporting Forage Intensification in Southwestern Uganda

Abstract ABSTRACT Sustainable livestock production in sub-Saharan Africa requires fodder intensification, yet baseline topsoil degradation and nutrient deficits remain unquantified across smallholder agro-ecosystems. This study evaluated topsoil (0-20 cm) physico-chemical properties and inter-parameter relationships across 58 smallholder fodder production gardens in the Southwestern Ugandan Cattle Corridor. Soil physical parameters (texture, bulk density) and chemical parameters (pH, organic matter, total nitrogen, available phosphorus, exchangeable K + , Na + , and Ca 2+ ) were characterized alongside spatial elevation data. Top soils were predominantly moderately to slightly acidic (mean pH = 6.18 ± 0.42), with 22.4% of plots falling below the critical threshold of pH 5.5, where aluminum phytotoxicity threatens root development. Soil organic matter was low-to-moderate (2.84 ± 0.81%) and positively correlated with exchangeable calcium (r = 0.312, p = 0.017), highlighting the role of organic complexes in maintaining cation exchange capacity. Macro-nutrient diagnostics revealed severe primary deficits: total nitrogen (mean 28.4 ± 9.2 ppm) and available phosphorus were critically limiting, with over 65% of plots exhibiting available phosphorus levels below 15 ppm. In contrast, exchangeable potassium levels were adequate (0.48 ± 0.22 cmol/kg) and demonstrated strong positive co-variance with available phosphorus (r = 0.538, p < 0.001), reflecting targeted household manure and organic amendment applications. Physical properties were dominated by coarse textures (sand 58.2 ± 11.4%), showing expected structural trade-offs between sand and clay (r = -0.692, p < 0.001) and sand and silt (r = -0.617, p < 0.001). Bulk density averaged 1.42 ± 0.16 g/cm3, with silt content acting as a major structural buffer that mitigated topsoil compaction (r = -0.346, p = 0.008).