Background Soil organic matter (SOM), playing an important role in increasing the stability of soil aggregates, effectively leads to a reduction of wind erosion. Soil calcium carbonate (CaCO₃), existing massively in the arid and semi-arid soil, also significantly affects soil wind erodibility. Thus revealing the content characteristics of SOM and CaCO₃ helps understand the process of wind erosion. Previous studies show that SOM has an effective role to play in the generation process of CaCO₃, thus there is a positive correlation between the content of SOM and CaCO₃. Due to the climate change and anthropogenic activities in Hulun Buir Sandy Land in the north China, desertification there tends to be inexorable and more severe than before.

Methods The study was conducted in the Hulun Buir Sandy Land. Total 93 sampling sites relating to mobile, semi-fixed and fixed sand dunes were located by GPS. Three sample plots nearby each sampling site were set up randomly. Aeolian topsoil (0~5 cm) were selected. SOM was determined using potassium dichromate volumetric method, while CaCO₃ was measured using a calcium ion concentration meter. Spatial variations of SOM and CaCO₃ were calculated and analyzed based on the theory of semi-variogram. Significant differences and correlation of data in different type of sand dunes were identified by SPSS16.0 statistical software, while spatial variation of that was analyzed by ArcGIS10.2 and GS+win10 software.

Results 1) The average content of SOM and CaCO₃ in the topsoil of Hulun Buir Sandy Land were 31.05 and 2.73 g/kg, respectively. During sand dune fixation, the content of SOM and CaCO₃ continuously increased. SOM content in mobile sand dunes was significantly lower than that in semi-fixed and fixed sand dunes, but CaCO₃ content in mobile sand dunes was just significantly lower than that in fixed sand dunes. 2) The content of CaCO₃ was positively correlative with the content of SOM by power function (R²=0.539, P < 0.01). While the content of CaCO₃ in mobile, semi-fixed and fixed sand dunes were also positively correlative with the content of SOM, with R² were 0.580, 0.630 and 0.245 respectively. With the increasing content of CaCO₃, the growth rate of SOM in fixed sand dunes was lower than that in mobile and semi-fixed sand dunes. 3) During sand dune fixation, the spatial variation of SOM and CaCO₃ were increasing, the distribution of SOM and CaCO₃ tended to be homogeneous, and the influence of random factors on the spatial variability of organic matter was getting more important. Structural factors of soil were the main cause of the spatial variation of SOM and CaCO₃ in Hulun Buir Sandy Land.

Conclusions During sand dune fixation, the decreasing intensity of soil erosion may influence the content, correlation and spatial variation of SOM and CaCO₃. The results of this study may provide theoretical reference for regional desertification combating and ecological restore.