Dataset for: Fixed-depth versus equivalent soil mass estimates of soil organic carbon stocks across major agricultural land uses in northeastern Thailand

This dataset supports the research article: Fixed-depth versus equivalent soil mass estimates of soil organic carbon stocks across major agricultural land uses in northeastern Thailand (submitted to Applied and Environmental Soil Science, Wiley). Study overview: Soil samples were collected in December 2025 from 50 agricultural fields in Mueang Chaiyaphum District, Chaiyaphum Province, northeastern Thailand (15.65–16.13°N, 101.81–102.24°E), with ten fields under each of five land uses: lowland paddy (PFL), upland paddy (PFH), sugarcane (SU), cassava (CA), and pineapple (AP). Each field was sampled at 0–15, 15–30, and 30–45 cm, yielding 150 observations. These are the minimum data required to reproduce the results of the article. Files included: sites.csv: site information (n = 50): land use, coordinates rounded to three decimal places (WGS 84), elevation, Land Development Department soil group and series, and USDA classification. soil_layers.csv: layer data (n = 150): organic carbon, pH, bulk density, sand, silt, clay, and USDA texture class. README.txt: variable definitions, units, methods, and notes for reuse. Key variables: organic carbon (% and g kg⁻¹; Walkley–Black), pH (0.01 M CaCl₂), bulk density (g cm⁻³; core method), sand, silt, and clay (%; hydrometer method), USDA texture class. Funding: Thailand Science Research and Innovation (TSRI), Fundamental Fund [grant number 216676].