Soil organic carbon and total nitrogen storage as affected by land use in a small watershed of the Loess Plateau, China

Soil organic carbon (SOC) is an important component of agricultural soil. Understanding the storage of carbon (C) and nitrogen (N) helps us understand how ecosystems would respond to natural and anthropogenic disturbances under different management strategies. Although the quantity of SOC stocks in the Loess Plateau has been previously investigated, the distribution and storage of C in its deep soil layers has been poorly studied to date. The present study was conducted in the Zhifanggou Watershed on the Loess Plateau to evaluate the effect of the types of land use on the distribution and storage of SOC and total nitrogen (TN) at different soil depths. Ten types of land use were investigated: woodland (Robinia pseudoacacia), shrubland (Caragana korshinskii; Hippophae rhamnoides), natural grassland, artificial grassland (Medicago sativa), orchard, check-dam cropland, terraced cropland (Setaria italica; Zea mays), and sloped cropland. The results show that land use significantly affects the SOC and TN content. The reconversion of sloped croplands into forestlands and grasslands improve their SOC and TN content. Natural grassland, terraced cropland with Z. mays, and the artificial grassland had the highest SOC content within 0–60 cm, 60–100 cm, and 150–500 cm layers, respectively. The SOC and TN content in the top layer were higher than those in the deep layer. Natural grassland had the highest SOC and TN storage within 0–40 cm layer, followed by shrubland I (C. korshinskii), check-dam cropland, woodland, and shrubland II (H. rhamnoides), orchard and artificial grassland, whereas the sloped cropland, and the terraced cropland with S. italica had the lowest values. The SOC and TN storage between the top (0–20 cm) and deep layers (0–100 cm, 0–300 cm, and 0–500 cm) can be modeled using linear function (y = ax + b). The results suggest that natural grasslands may be the optimal choice for SOC and TN sequestration in the Zhifanggou Watershed. Shrublands, woodland, artificial grasslands, orchards, terrace cropland with Z. mays and check-dam croplands are also recommended for their great contribution to SOC and TN storage in the area.

► The reconversion of sloped croplands into forestlands and grasslands improve SOC and TN content.
► SOC and TN content in the soil top layer were higher than those in the deep layer.
► SOC and TN storage between the top and deep layers can be modeled using linear function (y = ax + b).
►  Natural grasslands may be the optimal choice for SOC and TN sequestration in this region.