Spatial discrimination of salt- and sodium-affected soil surfaces

Salinization-alkalinization is a time- and space-dynamic soil degradation process in semiarid regions. This study implements a synergistic approach to map salt- and sodium affected surfaces, combining digital image classification with field observation of soil degradation features and laboratory determinations. Salinity-alkalinity classes were established using the electrical conductivity (EC) and pH values. A neighbourhood operator, with spatial and spectral user-defined constraints determined the spectral objects constituting the training set. Six combined Landsat TM bands (1,2,4,5,6,7) provided the highest separability between salt- and sodium-affected soil classes. Although the overall accuracy was slightly low (64 per cent), accuracies of 100 per cent were obtained for some classes. Main causes of spectral confusions, masking different salinity-alkalinity degrees were the type and abundance of salt-tolerant vegetation cover, the topsoil textures, and the mixture of topsoil properties under field conditions.