Characteristics of Soil Organic Matter and Carbon and Nitrogen Contents in Crops/Plants: Land Use Impacts

Change of land use is an important factor for the dynamics of soil organic matter and carbon and nitrogen cycles. Many parts of native land in the Yanqi Basin have been converted to cropland since 1950. To study the influence of land use change on carbon and nitrogen cycling, we collected plant and soil samples from 28 representative sites in crop and native land. Our results show a narrow range in carbon content (i.e., 44.2% in the native species and 41.7% in the crop species), but a large range in nitrogen content (0.3–3.9%). Plant C:N ratio may follow an order: native species (~31) < crops (~53), and aboveground tissues (~32) < belowground tissues (~52). Soil C:N ratio in native land (9.9) is closed to that in cropland. Both soil organic carbon and total nitrogen show a marked increase after long-term cultivation in Yanqi Basin, which may be associated with the increase of recalcitrant SOC.