Organic and Conventional Management Effects on Soil Organic Carbon and Macro-Nutrients Across Land Uses in the Bhutanese Himalayas

Soil health and fertility are essential components of sustainable land management. In Bhutan, where agricultural practices range from organic to conventional systems, and natural vegetation areas persist across varied elevations. Understanding how these factors influence soil properties is essential for advancing sustainable agriculture and fostering environmental stewardship. Thus, the objectives of this study were to evaluate some soil chemical properties across land use practices and their relationship to soil texture. Soil organic carbon (SOC) and macro-nutrients in three land use types (organic fields—OrgF; conventional fields—ConF; and natural vegetation—NatV) were studied across high-, mid-, and low-altitude sites in the Wangdue Phodrang, Chhukha, and Dagana districts of Bhutan. The effects of land use practices on soil properties varied with altitude. While available P responded significantly at both high- and mid-altitude locations (p < 0.01), SOC content was influenced only at high altitude (p < 0.001). In contrast, soil pH (p < 0.01) and available K (p < 0.001) showed clear sensitivity to land use at low altitude but were unaffected at higher elevations. Total N content and C:N ratios remained relatively stable across management practices within each altitude category. Silt and clay content had positive relationship with SOC (R2 ≥ 0.13), whereas sand content had a significant negative relationship (R2 = 0.23, p < 0.001). These findings are pertinent to providing guidelines for sustainable land management, improving agricultural practices, and shaping policies to protect and restore soil health across varied agro-ecological zones.