Particle-size fraction organic carbon and bulk soil properties in a three-year biochar chronosequence, longan orchards on acidic Ultisols, northern Thailand

Underlying data for a study of organic carbon in particle-size soil fractions (cPOM, fPOM, MAOM) across a 0-3 year chronosequence following a single field application of EM-inoculated longan-wood biochar (15 kg tree-1) in longan orchards on acidic Ultisols, Mae Pang, Phrao District, Chiang Mai, Thailand. Includes raw Walkley-Black titration data and recomputed organic carbon, and paired bulk-soil properties (SOC, texture, bulk density, pH, EC, water-extractable organic carbon, saturation indices). Companion elemental dataset: Aumtong et al. (2026) Scientific Reports 16, 22048 (doi:10.1038/s41598-026-59314-z). Version 2 adds a per-sample analysis-ready merged file (fraction OC joined to bulk properties and silt+clay) and a reproducibility script that regenerates all headline statistics.