A multi-decadal assessment dataset of soil organic matter in the Sanjiang Plain black soil region (1984–2023)

Accurate estimation of soil organic matter (SOM) content in cultivated land is essential for food security and climate change mitigation. Here we present SOM-SJP-40y, a 40-year (1984-2023) dataset of topsoil SOM dynamics for the Sanjiang Plain, a typical black soil region in China. The dataset integrates 364 field samples (0-20 cm) with decadal median composites of bare soil imagery derived from Landsat time series on the Google Earth Engine platform. SOM predictions were generated using a probabilistic hybrid modeling approach combined with K-means clustering, achieving a model performance of R² = 0.72, RMSE = 8.66 g kg⁻¹, and RPD = 1.75. Using SOM-SJP-40y, we observe spatially heterogeneous SOM dynamics, with localized SOM increases in some areas since the 2010s that may be associated with recent conservation policies. This dataset offers a valuable resource for soil quality assessment, farmland protection, and carbon management in black soil regions.