Spatial variations of organic matter concentration in cultivated land topsoil in North China based on updated soil databases

Abstract

Accurate knowledge of spatial variations in organic matter concentration of cultivated land topsoil (CTSOM) is crucial for the effective use and management of cultivated land. However, this knowledge remains largely uncertain owing to outdated and imprecise soil databases. Therefore, in 2020, this study meticulously collected 918 samples of cultivated land topsoil (0–30 cm) in Hebei Province of North China, and a Random Forest (RF) model was used to delineate the spatial variability of CTSOM. Results indicated the robust performance of the RF model containing 21 predictors, with an R2 of 0.77, and soil total nitrogen (TN) emerging as the most important predictor. The current mean CTSOM level in the study area stood at 16.47 ± 3.94 g kg−1, displaying a spatial pattern with higher CTSOM levels in the western and northern mountainous areas, and lower levels in the eastern plain areas. A comparison with the second national soil survey data revealed that the overall regional level of CTSOM has increased by 4.28 g kg−1 over the last 40 years. However, a significant decline in CTSOM was observed in the northern part of the study area, where straw return and fertilization can be key contributing factors. This study provides updated knowledge on the spatial variations of CTSOM in North China, which is valuable for agricultural ecosystem management worldwide and for carbon accounting in terrestrial ecosystems.