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

Gábor Szatmári 1,2, Zsófia Bakacsi 1, Annamária Laborczi 1,*, Ottó Petrik 3, Róbert Pataki 3,
Tibor Tóth 1 and László Pásztor 1

1 Institute for Soil Sciences and Agricultural Chemistry, Centre for Agricultural Research,
H-1022 Budapest, Hungary; szatmari@rissac.hu (G.S.); zsofi@rissac.hu (Z.B.); tibor@rissac.hu (T.T.);
pasztor@rissac.hu (L.P.)
2 Department of Soil Science and Environmental Informatics, Georgikon Faculty, Szent István University,
H-8360 Keszthely, Hungary
3 Lechner Knowledge Center, H-1149 Budapest, Hungary; otto.petrik@lechnerkozpont.hu (O.P.);
robert.pataki@lechnerkozpont.hu (R.P.)


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 saltaffected 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.