Characteristics of soil organic carbon at 38°N ecological transect of Hebei Province

To understand the characteristics of organic carbon in the 38°N ecological transect of Hebei Province, 35 sampling plots with different land use patterns in 3 regions (low hilly area, piedmont plain of Taihang Mountain and low coastal plain) in the 38°N ecological transect of Hebei Province from west to east were set and soil samples were collected in the 010 cm, 1020 cm, 2040 cm, 4060 cm and 60100 cm layers from September to October in 2011 for soil organic carbon content analysis. The results suggested that the soil organic carbon density was higher in the low hilly area than in the piedmont plain, which was in turn higher than in the low coastal plain. The corresponding soil organic carbon density was respectively 9.03 kgm^-2, 4.26 kgm^-2 and 3.51 kgm^-2. The difference in organic carbon content of the low hilly area from that of other two regions was partly due to the high organic carbon content in scrublands in the low hilly area. Furthermore, organic carbon content in the 040 cm soil in forestland and farmland in the low hilly area was higher than those in the other two regions. The order of soil organic carbon content in forestland and farmland was low hilly area > piedmont plain > low coastal plain. Organic carbon content in 040 cm soil in forestlands was 19.45 gkg^-1 (low hilly area), 7.89 gkg^-1 (piedmont plain) and 7.55 gkg^-1 (low coastal plain). Also soil organic carbon content in farmland was 7.70 gkg^-1 (low hilly area), 7.09 gkg^-1 (piedmont plain) and 6.00 gkg^-1 (low coastal plain). Soil organic carbon content decreased with soil depth and there was some difference among different land use patterns. The sequence of variation in soil organic carbon content with soil depth (from top to bottom) was higher in the low hilly area than in the piedmont plain, which was in turn higher than in the low coastal plain. In the low hilly area, the variation range of soil organic carbon content with soil depth was higher in scrubland than in forest, and it was lowest in farmland. In the piedmont plain, the range of variation in soil organic carbon content with soil depth in farmland was a slight bigger than that in forest land. In the low coastal plain, the range of variation in soil organic carbon content with soil depth was higher in forest land than in abandoned land, it was lowest in farmland. In consideration of carbon sequestration and economic benefits, 3 suggestions were put forward as follows: 1) forest products and tourism should be developed in the low hilly area; 2) the piedmont plain should emphasize the development of grain production; and 3) the low coastal plain should be improved in soil salinization and cotton cultivation.