Preliminary Study On Soil Salinity Distribution And The Factors In Hetao Irrigation District

Based on field investigation and soil sampling, this thesis studied the spatial variability of surface soil salinity in the Hetao Irrigation District in the Inner Mongolia, China using methods of descriptive statistical analysis and geostatistical analysis; we investigated both the natural and human factors that lead to spatial variation of soil salinity in the study area. Findings from this research may provide scientific basis for prevention and amelioration of salinized soils in arid regions. Major findings of this research are as below:(1) Statistical analysis showed that the salt content of the surface soil (0-15cm) is log-normally distributed with a strong variability; the groundwater depth is normally distributed with a medium variability. Based on the principle of geostatistics, the measured data of groundwater salinity in the Hetao Irrigation District comply with a normal distribution, and the groundwater salinity of the watershed has significant spatial and temporal variability.(2) Semi-variogram analysis showed that the nugget coefficients for the surface soil salinity, groundwater depth and groundwater salinity in April and July 2014 are 20%,18%,18%,15%, 24%and 15%, respectively, and they are strongly correlated spatially, indicating that they are greatly influenced by the spatial variability of the region, and the regional structural factors are more evident.(3) From the spatial scale, the surface soil salinity increased with decreasing water table depth; the groundwater salinity is not correlated with the spatial variation of soil salinity. From the temporal scale, the groundwater depth in July is smaller than that in April, and the soil salinization has a tendency to increase. The area with saline groundwater of>5g/L is little affected by seasons, while the areas with groundwater salinity less than>5g/L changed with seasons significantly.(4) The long-term average salt input of the irrigation area is greater than the salt output, indicating a salt accumulation state. In the same planting years, soil salinity changed with the land use, salinity changes are woodland> grassland> farmland.. Within the same land use, planting age is inversely proportional to the soil salt contents, with the increase of the planting age, the reduction in soil salinity decreased. The surface accumulation of salt in the woodland is relatively obvious, In the grassland and farmland, soil salinity of the surface layer is lower than that in the bottom layer, and salts are mainly accumulated in the depths of 20 to 60cm.(5) The difference in spatial distribution of soil salinity in the Hetao Irrigation District is mostly influenced by the spatial distribution of groundwater depth, soil type and texture, land use, cropping pattern and the irrigation processes.