Influence of altitudinal zones on soil nutrient dynamics and fertility constraints in agricultural terrains of Yunnan, China

Altitudinal variation influences soil fertility by modifying climate and geomorphic conditions across elevation bands. This study analyzed 350 surface soil samples (0-30 cm) collected from four elevation zones (1600-2000, 2000-2400, 2400-2800, and > 2800 m) in cultivated areas of Yunnan Province, China. Each sample was tested for texture, pH, electrical conductivity (EC), calcium carbonate (CaCO₃), organic matter (OM), total nitrogen (TN), available phosphorus (AP), available potassium (AK), and micronutrients (Fe, Mn, Zn, Cu). The soils were generally alkaline (mean pH 7.9; range 7.3-8.4) and poor in organic matter (mean 1.2%), especially above 2800 m. Total nitrogen was very low (mean 0.06%), and 45-75% of samples were deficient in available phosphorus. Potassium levels were moderate to high (mean 420 mg/kg). Iron and copper were deficient in over 90% and 60% of samples, respectively, while zinc was sufficient at lower elevations. Comparing two classification methods showed that the Gomez approach provided finer, elevation-specific distinctions, whereas the Common method offered simpler, management-oriented groupings. One-way ANOVA indicated no significant differences in most soil properties across elevations (p > 0.05), with only a marginal effect for phosphorus (p = 0.076). Overall, alkaline pH, low organic matter, and nutrient deficiencies are the main fertility constraints in Yunnan's agricultural soils. Although statistical differences among elevation zones were small, subtle trends highlight the need for locally adapted nutrient management rather than uniform, elevation-based strategies to sustain productivity in mountainous regions.