Quantitative evaluation of soil salinity and its spatial distribution using electromagnetic induction method

In the Lower Yellow River Delta, soil salinity is a problem due to the presence of a shallow, saline water table and marine sediments. Spatial information on soil salinity at the field level is increasingly needed, particularly for better soil management and crop allocation in this area. In this paper, a mobile electromagnetic induction (EMI) system including EM38 and EM31 is employed to perform field electromagnetic (EM) survey, and fast determination and quantitative evaluation of the spatial pattern of soil salinity is discussed using the field EM survey data. Optimal operation modes of EM38 and EM31 are determined to establish multiple linear regression models for estimating salinity from apparent soil electrical conductivity (EC_a). Spatial trend and semivariogram are illustrated and spatial distribution of field salinity status is further visualized and quantitatified. The results suggest that EC_a (EM38 and EM31) data is highly correlated with salinity, and that the interpretation precision of soil salinity at various layers can be improved using EM_38h and EM_31h (where h represents the horizontal mode of EM measurement). Both EM_38h and EM_31h exhibit significant geographic trend. Nested spherical models fit the semivariance of EM_38h and EM_31h better than single spherical models. Spatial autocorrelation of EM_31h is stronger than that of EM_38h, and short-range variation is the chief constitute of spatial heterogeneity for both EM_38h and EM_31h. Quantitative classification shows that soil salinity exhibits the trend of accumulation in the root zone. In 0-1.0 m solum, heavy salinized and saline soils are the predominant soil types, accounting for 54% and 41% of total survey area, respectively. The area of light and moderate salinized soils is comparatively small, which accounts for only 0.4% and 4.6%, respectively.