Prediction of temporal and spatial soil salinity distributions using electromagnetic conductivity imaging and regional calibration
摘要
In this study, the potential of using electromagnetic induction (EMI) and in situ regional calibration for predicting the electrical conductivity of saturated soil paste extract (ECe) over relatively large spatial and temporal scales in a salt-affected agricultural area in northern Egypt was evaluated. The apparent electrical conductivity (ECa) was measured using a CMD2 electromagnetic induction instrument in three agricultural plots with ECe values ranging from 5.29 to 115.00 dS m−1. The ECa data were inverted to generate electromagnetic conductivity images (EMCIs) to provide the spatial distribution of the true soil electrical conductivity (σ) with depth (i.e., 90 cm). Based on the observed ECe, a regional calibration equation was developed. Its prediction ability was validated by performing new measurements (i.e., a second measurement campaign) in the same plots one month later and in four new plots with similar soil conditions (i.e., a third measurement campaign) approximately one year after the first campaign. The four new plots were located approximately 1.5 km away from the three original plots. The results showed that the developed regional calibration equation accurately predicted the ECe with an R2 of 0.95. The prediction ability was also high, with an RMSE and R2 of approximately 8.70 dS m−1 and 0.92, respectively, for the validation subsets. Thus, the derived regional calibration equation is reliable and can be used for mapping soil salinity over relatively large spatial and temporal scales in this region without any further calibration. As soil is classified as moderately to severely saline, the proposed technique can be used to improve agricultural management by providing reliable assessments of soil salinity in the study area and other similar agrosystems.