Digital Mapping of Gypsic Horizon Morphotypes and Soil Salinity in an Old Alluvial Piedmont Plain of Uzbekistan

Abstract

The digital maps of soil salinity, gypsum, and gypsum pedofeatures in soils (gypsic calcisols, gypsisols, and solonchaks) of the Dzhizak experimental station (Uzbekistan) are compiled from the results of soil survey conducted during 1980 and 2008, using digital elevation model (DEM) and remote sensing data. The study area represents a part of the Golodnaya Steppe piedmont plain to the north of Turkestan ridge. The macro- and micromorphological descriptions of gypsic horizons made it possible to distinguish three different morphotypes. The morphological features of gypsic horizons were classified, and their distribution map was prepared using GIS tool. The spatial distribution of different morphotypes of gypsic horizons showed distinct correlations with the soil salinity, the groundwater level, and the character of soil water regime. It was established that the presence of different gypsic horizons should be taken into account in the new substantive-genetic classification of Russian soils at high taxonomic levels. Studies completed after 20 years, when the groundwater level dropped by about 1 m, confirmed that the gypsum content decreased in soils; however, the major morphotypes were preserved. The micromorphological investigations demonstrated that certain changes took place in the microfabric of gypsum pedofeatures. Thus, fine dispersed crystals of gypsum disappeared from the soil profiles, and the number of pseudomorphic substitutions of calcite for gypsum crystals increased significantly attesting to the progressive calcification of soil profiles.