Elaborating Hungarian Segment of the Global Map of Salt-Affected Soils (GSSmap): National Contribution to an International Initiative

Gábor Szatmári,Zsófia Bakacsi,Ottó Petrik,László Pásztor,Róbert Pataki,Tibor Tóth,Annamária Laborczi

doi:10.3390/rs12244073

Abstract

Recently, the Global Map of Salt-affected Soils (GSSmap) was launched, which pursued a country-driven approach and aimed to update the global and country-level information on salt-affected soils (SAS). The aim of this paper was to present how Hungary contributed to GSSmap by preparing its own SAS maps using advanced digital soil mapping techniques. We used not just a combination of random forest and multivariate geostatistical techniques for predicting the spatial distribution of SAS indicators (i.e., pH, electrical conductivity and exchangeable sodium percentage) for the topsoil (0–30 cm) and subsoil (30–100 cm), but also a number of indices derived from Sentinel-2 satellite images as environmental covariates. The importance plots of random forests showed that in addition to climatic, geomorphometric parameters and legacy soil information, image indices were the most important covariates. The performance of spatial modelling was checked by 10-fold cross validation showing that the accuracy of the SAS maps was acceptable. By this study and by the resulting maps of it, we not just contributed to GSSmap, but also renewed the SAS mapping methodology in Hungary, where we paid special attention to modelling and quantifying the prediction uncertainty that had not been quantified or even taken into consideration earlier.

Highlights

In the past decade, a number of international initiatives have been launched in order to provide thematic spatial soil information with relatively high resolution at the global scale, e.g., SoilGrids [1], Global Soil Map [2] and Global Soil Organic Carbon Map [3]
A terser summary is given in Figure 2 in which the importance of a given environmental covariate was presented by counting its occurrence on the list of the top 3, 5, 10, and 20 important covariates of each Salt-affected soils (SAS) indicator
Hungary is located in the Carpathian Basin, and Hungarian salt-affected soils have been mainly formed in the Great Hungarian Plain, which are discharge areas of regional flow systems of groundwater characterized by surplus salts and especially sodium ions

Summary

Introduction

A number of international initiatives have been launched in order to provide thematic spatial soil information with relatively high resolution (from 1 km to 100 m) at the global scale, e.g., SoilGrids [1], Global Soil Map [2] and Global Soil Organic Carbon Map [3]. A country-driven (a.k.a “bottom-up”) approach is frequently pursued in which a given country is invited to prepare its own thematic soil maps for targeted soil properties and functions according to the specifications summarized in a guideline or “cookbook” (e.g., [3,4]). This approach has its own advantages and disadvantages, e.g., a map prepared by a country could be more accurate than a globally or continentally compiled one [5,6]. The global map of GSSmap is expected to be published in December, 2020

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