Effects of land use changes on soil organic carbon, nitrogen and their losses in a typical watershed of the Loess Plateau, China

The "Grain for Green" programme has had a significant impact on land use change and carbon and nitrogen balance. However, it is unlear how vegetation restoration affects soil organic carbon (SOC), nitrogen (N) and their losses based on the grid measured data of regional scale. In this study, at the watershed scale, the SOC, N, nutrient losses, sequestration rates, sequestration potential, and influencing factors of croplands, orchards, grasslands, forests and human settlements were assessed through 113 sampling points. Results showed that natural vegetation soil exhibited the highest SOC storage (38.9 Mg center dot ha- 1) and N storage (0.86 Mg center dot ha- 1), and grasslands had the highest SOC sequestration rate (19.2 kg center dot hm- 2 center dot yr- 1) and N sequestration potential (5.7 kg center dot yr- 1). Additionally, forests had the highest SOC sequestration rate (0.43 Mg center dot hm- 2 center dot yr- 1), and orchards had the highest SOC sequestration potential (161.2 Mg center dot yr- 1). The SOC storage, N storage, and sequestration potential of artificial vegetation were mainly affected by the soil particles and bulk density, however, the SOC storage, N storage, and sequestration potential of natural vegetation were mainly affected by the soil aggregate stability and soil C: N. In addition, the heaviest losses of SOC and N occurred in grasslands, with the highest average amounts in orchards, and the lowest average amounts in forests. We put forward general management suggestions for different vegetation types and focus on four measures for the management of orchards, with a view toward reducing SOC and N losses in different land use types.