The estimation of soil organic carbon distribution and storage in a small catchment area of the Loess Plateau

The distribution and storage of soil organic carbon serve as basic data for the study of soil productivity, soil hydrological properties, and the balance among carbon-based greenhouse gases. In this study, the organic carbon storage and density distribution characteristics of the soil in the Zhifanggou catchment on the Loess Plateau were studied based on field investigations, laboratory measurement, and geostatistics analysis. A total of 1,282 soil samples were collected from 215 sites in addition to 10 profiles from the catchment. The landuse within the catchment was divided into 4 types: farmland, grassland, shrubland, and woodland. The following results were obtained. 1. In the Zhifanggou catchment, the average organic carbon content of the soil at a depth of 0–100 cm is between 2.81 and 3.50 g·kg− 1. The soil organic carbon content (SOCC) for different landuse types follows the trend shrubland > woodland > grassland > farmland, whereas the soil bulk density follows. The relationship between soil organic carbon content and bulk density follows a power law function. 2. The soil organic carbon density (SOCD) at a depth of 0–100 cm is 1.24–8.34 kg m− 2. The coefficient of variation is 0.40, indicating a moderate variation in the average carbon density of 2.63 kg m− 2. The soil organic carbon density for different landuse types follows the trend shrubland > woodland > grassland > farmland. In the entire catchment, the proportion of average soil organic carbon density at a depth of 0–20 cm is 50.24%, which decreases with soil depth. The spatial distribution of the soil organic carbon density is closely related to the landuse types and topography. 3. The total soil organic carbon storage (SOCS) at a depth of 0–100 cm in the Zhifanggou catchment is 21.84 × 106 kg. The relationship between soil depth and total organic carbon storage is linear.

► The soil organic carbon (SOC) content is between 2.81 and 3.50 g kg− 1.
► The changes of the SOC content show a moderate variation.
► The SOC density shows a ladder-like pattern and patch mosaic distribution.
► The SOC storage of the catchment at a depth of 0–100 cm is 21.84 × 106 kg.