Effect of grazing on wind driven carbon and nitrogen ratios in the grasslands of Inner Mongolia

Wind erosion and dust storms are common phenomena in the semi-arid Xilingele grassland (Inner Mongolia) and contribute considerably to matter balances. Dust emission and dust deposition affect particles of the silt and clay fraction and the organic matter predominantly. the carriers for nutrients in soils. Based on wind erosion measurements in spring 2005 and 2006 the organic carbon and total nitrogen contents of dust were analyzed to determine the contribution of wind erosion processes on C- and N-ratios to the grasslands. Dust deposition is important for the C and N balance in semi-arid grasslands. Despite large differences in dust storm intensities. the C-org and N-t contents in the trapped sediments were in the same range for both years with 35.1-39.1 mg g(-1) (C-org) and 3.23-3.60 mg g(-1) (N-t). These contents were significantly higher than the average soil contents of C-org and N-t which were 24.5 mg g(-1) and 2.53 mg g(-1), respectively. Grazing intensity was the strongest influencing factor on material gains or losses and was reflected strongly in the vegetation conditions (vegetation height and vegetation coverage). A moderate grazing with 1 to 2 ewes per hectare was the grazing practice, in which dust deposition and dust emission were in equilibrium. Heavy grazing (> 2 ewes per hectare) resulted in average organic carbon and nitrogen losses of 4.8 kg ha(-1) (C-org) and 0.4 kg ha(-1) (N-t) in the spring 2005 and 89.8 kg ha(-1) (C-org) and 8.3 kg ha(-1) (N-t) in the spring 2006. Lightly grazed sites (< 1 ewe per hectare) gained between 14.7 and 52.7 kg ha(-1) C-org and 1.4 to 4.8 kg ha(-1) N-t in 2005 and 129 to 243 kg ha(-1) C-org and 11.9 to 22.3 kg ha(-1) N-t in 2006. The largest matter gain was measured at ungrazed sites with on average 238.9 kg ha(-1) C-org and 20.0 kg ha(-1) N-t in 2006. (C) 2008 Elsevier B.V. All rights reserved.