SPATIAL DISCRIMINATION OF SALT-AFFECTED AND SODIUM-AFFECTED SOIL SURFACES

Salinization-alkalinization is a time- and space-dynamic soil degradat ion process in semiarid regions. This study implements a synergistic a pproach to map salt- and sodium affected surfaces, combining digital i mage classification with field observation of soil degradation feature s and laboratory determinations. Salinity-alkalinity classes were esta blished using the electrical conductivity (EC) and pH values. A neighb ourhood operator, with spatial and spectral user-defined constraints d etermined the spectral objects constituting the training set. Six comb ined Landsat TM bands (1,2,4,5,6,7) provided the highest separability between salt- and sodium-affected soil classes. Although the overall a ccuracy was slightly low (64 per cent), accuracies of 100 per cent wer e obtained for some classes. Main causes of spectral confusions, maski ng different salinity-alkalinity degrees were the type and abundance o f salt-tolerant vegetation cover, the topsoil textures, and the mixtur e of topsoil properties under field conditions.