Abstract
Electrical conductivity (EC) is an important index of soil salinity level and an essential factor in judging whether improvement can be made and assessing the improvement, if any. However, saline soils of different types show different spectral characteristic bands, which affects the retrieval precision to a certain extent. To tackle this issue, we present a novel way of modeling. Specifically, we compare the correlation of sensitive bands, multiplication of sensitive bands, and spectral indexes with EC data to determine the optimal input parameters, and take the EC data after Box-Cox transformation as the output. We then try out several machine-learning algorithms to establish retrieval models for soil EC. Validation results show that the model precision increases by 3.23–85.71% after EC data transformation and machine learning models produce 29.41–86.67% higher precision than the linear regression model. Finally, using the optimal model, we retrieve pixel-level (10 m × 10 m) EC for the soil in our study areas. This provides necessary data support for working out soil desalinization initiatives and evaluating the effectiveness of such initiatives.
Highlights
S Saline-sodic soil is a collective term which can refer to saline soil and sodic soil at any salinity level
Davis et al (2019) used Landsat OLI and Sentinel-2 MSI to reverse the conductivity of saline soil, and the results show that MSI is superior to OLI and that the visible light band is more sensitive to soil salinity
We calculate the coefficient between the training dataset and the spectral reflectance of each band, which is extracted from Sentinel-2 MSI data, and determine the sensitive bands based on the coefficient values
Summary
S Saline-sodic soil is a collective term which can refer to saline soil and sodic soil at any salinity level. Saline soil is soil that contains soluble salt at a high level so that crops will be severely impacted. The specific salinity level depends on the type of salt content. Sodic soil is soil that contains exchangeable sodium that negatively affects crops and alters the attributes of soil. Saline-sodic soils come in different types in that their parent materials and the natural conditions to form them are different. Depending on the types of salt content in the soil, saline-sodic soils are classified into six types: pure soda soil, soda soil, chloride soil, sulfate chloride soil, chloride sulfate soil, and sulfate soil. Soil salinization and secondary salinization are thorny problems faced by the whole world. It’s estimated that 6% of the world's terrestrial land is primarily salinized and about 20% of cropland and 30% of irrigated land is secondarily salinized, totaling about 1 Bha globally (Lian et al, 2010)
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