PARENT SESSION
Poster Session 7: Grasslands
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Changes in soil organic carbon and nitrogen of a chernozem in responses to land use in Xilin River basin, China.

Wang, Qibing¹, Han, Xingguo¹, Li, Linghao¹, Xing, Xuerong¹, Bai, Yongfei¹, Cao, Jirong¹, ¹ Institute of Botany, Beijing, CHINA

ABSTRACT- Grasslands may be an important sink for atmospheric CO2, as they cover 40 percent of the earth's surface and store about one-third of the global terrestrial C stock, with most of it in their soils. The decrease in soil organic C (SOC) stock from converting natural grasslands to agriculture is well recognized, but its magnitude remains uncertain because of variable land use, management practices and ecological factors. Meadow steppe, one of the major vegetation types in the Xilin River basin, China, is rich in SOC. A large area of this ecosystem has been converted to cropland over the past half-century, but the changes in SOC and soil nitrogen (N) have not received much attention. We examined the effects of land use on SOC and N along a land use chronosequence that included three treatments: (1) uncultivated meadow steppe (meadow steppe); (2) 28-yr plow conversion of meadow steppe to cropland (28-yr cropland); (3) 42-yr plow conversion of meadow steppe to cropland (42-yr cropland). Soil samples from three depth increments (0-10, 10-20, 20-30 cm) were analyzed for SOC, total N, and 2M KCl-extractable inorganic N (NH+4-N and NO-3-N + NO-2-N). Cultivation significantly decreased SOC and total N throughout the entire 0-30 cm depth interval, with losses of 9.83 Mg C ha-1 (10.8%)and 0.66 Mg N ha-1 (8.8%) in the 28-yr cropland soil, and 21.87 Mg C ha-1 (24.1%) and 1.18 Mg N ha-1 (15.7%) in the 42-yr cropland, relative to the meadow steppe. This suggests that soil C losses from current land-use change in the region studied may be less than those in other biomes. The greatest losses were found in the depth of 0-10 cm (> 90% in the 28-yr cropland and > 65% in the 42-yr cropland for the SOC); At this depth, it contributed even more to the overall loss of total N, however, inorganic N contents were 30.6% for 28-yr cropland and 26.9% for 42-yr cropland higher than that in the soil under the natural meadow steppe. These results indicate that the conversion of natural meadow steppe to agriculture leads to net losses of SOC and total N, proper management practices that can preserve SOC and N should be implemented for mitigation of greenhouse effects and grassland sustainable use.

Key words: land use change, meadow steppe, soil organic carbon, nitrogen