Sodium- and salt-affected soils extend well over 10 million hectares in the Northern Great Plains (NGP) of the USA. Levels of soil sodicity and salinity vary spatially across the landscape; vertically with soil depth, and temporally; making it difficult to characterize, classify, and manage these soils. Laboratory measurements are relatively time-consuming and costly to obtain, and are therefore limited in number. Surrogate field measures of apparent electrical conductivity (ECa) obtained with electromagnetic induction (EMI) are being evaluated to improve the classification, mapping, Interpretation and management of these soils in the NGP. This paper examines the use of EMI with the ESAP (ECe Sampling, Assessment, and Prediction) software program to predict and map the variability of soil sodicity and salinity at field scales. Large ECa data sets were collected across four fields located within the Rolling Soft Shale Plain resource area of southwestern North Dakota. these data sets were used with the ESAP-RSSD (response surface sampling design) program to locate a minimum number of soil sampling (calibration) sites within each field where soils were sampled for laboratory characterization. Geo-referenced ECa and soil profile characterization data were used to calibrate appropriate predictive equations for soil sodicity and salinity and to estimate the spatial variability of both properties. At all sites, soils became more sodium-affected and saline with increasing depths. for the 0 to 90 cm depth interval (primary rooting zone), soils were dominantly saline (>4 dS/cm) non-sodic (SAR <13) and saline-sodic (>4 dS/m and SAR >13). However, inclusions of non-saline (<4 dS/m) and non-sodic (SAR <13) soils occurred in each unit of management. Simulations were use to characterize spatial patterns of soil sodicity and salinity. This methodology shows promise for improving the understanding of soil-landscape relationships and impacting the classifications and Interpretations for sodium-affected and saline soil map units in the NGP.


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