[Spatial variability of soil properties in fixed sand dunes of the Eastern Ningxia Province]. / 宁夏东部风沙区固定沙丘土壤性质小尺度空间变异特征.

As sand dunes gradually become fixed, soil particle size, soil organic carbon (SOC) and total nitrogen (TN) contents vary across different locations of the dunes. To investigate the spatial variation of soil particle size distribution and soil nutrition in the fixed sand dunes, we examined particle composition, SOC and TC features in different locations of dunes in the Eastern Ningxia. The results showed that the particle sizes of each soil layer were mainly characterized by medium and coarse sands. The SOC and TN contents were higher in surface soil layers, with a maximum of 5.781 and 0.412 g·kg-1, respectively, which were observed in interdune lands and dune ridges, while the leeward slope of the dunes showed the least. The SOC content of both the leeward and windward slope gradually decreased with increasing soil depth along the dune. By contrast, that of the interdune lands decreased first and then increased. At small scale, both the SOC and TN contents showed a clear spatial heterogeneity. There was a positive correlation between soil nutrition contents (SOC and TN) and silt and very fine sand contents in the fixed sand dunes, and a negative correlation with medium and coarse sand contents. Our results implied that soil particle size composition influenced SOC and TN contents. The contents of soil nutrition increased with increa-sing contribution of fine particles, highlighting the role of fine particles in adhesion and accumulation of organic matter.

[Surface erosion-resistance of Nitraria tangutorun nebkhas at different succession stages in Minqin oasis and related affecting factors].

By measuring the surface shear strength of Nitraria tangutorun nebkhas at different succession stages in the fringe of Minqin oasis, and selecting several typical nebkhas at stabilizing stage to investigate its surface erosion rates before and after removing crust and vegetation, the surface erosion-resistance of N. tangutorun nebkhas and related affecting factors were studied. The results showed that the nebkhas had the highest surface shear strength (0.31-0.79 kg cm(-2)) at stabilizing stage, and the lowerest one (0.06-0.15 kg cm(-2)) at rudimental stage. The surface shear strength of nebkhas at stabilizing stage was significantly higher than that at other succession stages (P <0.01), and at the other succession stages except degradation stage, there was no significant difference in the surface shear strength in windward and leeward (P >0.05). After removing crust and vegetation, the surface shear strength of nebkhas at stabilizing stage was greatly reduced, with the difference before and after removing the crust and vegetation being significant (P <0.01). However, there was no obvious difference between different slope positions (P >0.05). Keeping both vegetation and crust, deposition occured on both slope positions of nebkhas; removing crust but keeping vegetation, the deposition reduced a little; removing vegetation but keeping crust, the deposition reduced greatly; while removing both vegetation and crust, nebkhas surface was severely eroded.