MONITORING AND THE STUDY OF THE EFFECTS OF IMAGE SCALE ON DELINEATION OF SALT-AFFECTED SOILS IN THE INDO-GANGETIC PLAINS

The study was carried out (i) to monitor the spatial extent of salt-affected soils and (ii) to assess the effect of image scale on the delineation of these soils using Landsat data in the Indo-Gangetic plains of Uttar Pradesh, northern India. Monoscopic visual interpretation of standard false colour composite (FCC) prints of Landsat-MSS data acquired in 1975 and of Landsat-TM data acquired in 1986 was carried out to delineate salt-affected soils during these two periods. Salt-affected soils could be categorized as saline sodic soils and key out as Typic Natrustalfs. A shrinkage in the areal extent of salt-affected soils to the extent of 9.9 per cent was observed during an 11-year period which could be attributed to ameliorative efforts by the farmers and to state and central Government agencies. The effects of image scale on the delineation of salt-affected soils was studied by visually interpreting the standard FCC prints of TM data at the 1:250 000 scale and for the same area at the 1:50 000 scale, refinement of the boundaries of salt-affected soils delineated at the 1:250 000 scale, could be achieved. In addition, small pockets of salt-affected soils occurring within normal soils could be detected on a Landsat-TM FCC print at the 1:50 000 scale. Detailed methodology and morphological and physico-chemical characteristics of salt-affected soils are also given.