Based on soil organic matter (SOM) data from the Ebinur Lake Basin in the Xinjiang Uygur Autonomous Region of western China and three-way ANOVA we analyzed whether SOM content was significantly influenced by three factors: the soil type, the vegetation type and the soil depth. A semi-variogram and Ordinary Kriging (OK) models were then used to study the spatial variability of the SOM at different soil depths. Finally, the vertical spatial variations of the SOM were investigated using the empirical orthogonal function (EOF) decomposition. Ebinur Lake is a rift lake in northwest China near the border with Kazakhstan. Vegetation types vary from low hygrophyte salt-tolerant shrubs to tall drought-tolerant Populus euphratica forests and grow on clay, loam, and sand soils.
The results of ANOVA show the vegetation type significantly affects the SOM content, but the soil type and soil depth have not influenced SOM content in a statistically significant manner. The results of the semi-variogram and Ordinary Kriging analysis show spatial variability of SOM content exhibits different characteristics with changes in soil depth; also the high- and low-SOM content regions display a patchy pattern in the 0-80cm soil layer in the Ebinur Lake Basin. However, the SOM content changes are relatively continuous in the 80-120cm soil layer, and the SOM content is higher in the eastern and western parts of the region than in the central region of the Ebinur Lake Basin. The spatial variation patterns satisfy the hole model in the 0-80cm soil layer, while the exponent model is fitted well in the 80-120cm soil layer in the semi-variogram. Also, the results of the EOF analysis illustrate the vertical spatial distribution of SOM shows different characteristics with the soil depth across the Ebinur Lake Basin. Specifically, the SOM content decreases as the soil depth increases in the central part of the Basin. In that area, SOM content drops gradually from 2.85g/kg in the 0-20cm soil layer to 1.51g/kg in the 100-120cm soil layer. However, the SOM content displays an increasing trend with increasing soil depth in the eastern and western regions of the Ebinur Lake Basin. Specifically, the SOM content increased substantially from 1.80g/kg in the 0-20cm soil layer to as much as 6.61g/kg in the 100-120cm soil layer in the western region, and the SOM content increased gradually from 1.04g/kg in the 0-20cm soil layer to 2.86g/kg in the 100-120cm soil layer in the eastern region of the Basin.
In the Ebinur Lake Basin, the patterns of spatial variation in the SOM are extremely significantly different between the shallow soil layers when compared to the deeper soil layers, and this characteristic is strongly relevant to the patches of the arid oasis ecological landscape and the features of the vegetation rhizodeposition. Also, the spatial heterogeneity during evolution of the soil profiles in the Basin suggests a significant restraining effect on vertical spatial variability of the SOM with soil depth. Our results provide a scientific basis for rational land use, vegetation protection and the ecological restoration policy-making process in the Ebinur Lake Basin.