MONITORING CHANGE IN THE EXTENT OF SALT-AFFECTED SOILS IN NORTHERN INDIA

A large area of barren salt-affected soils has been reclaimed in recent years in the Ganges Plains of Uttar Pradesh, India. Increased canal irrigation in the area, on the other hand, is also leading to salinization of new areas. A study was conducted using aerial photographs and Landsat Thematic Mapper (TM) data to monitor change in the status of salt-affected soils in the Kanpur district of Uttar Pradesh. Old survey maps prepared using ground methods in 1956, showing large salt-affected soil blocks of more than 80 ha, were used as a basis for comparison. These maps were compared with the maps prepared using aerial photographs of 1972 and Landsat TM images of 1986. Aerial photographs on a 1:40 000 scale and standard Landsat TM false colour composite (FCC) image on 1:50 000 scale provided a minimum delineation of 2 ha size, which was considered sufficient for change detection in the present case. The average increase in cultivation due to reclamation within the salt-affected soil blocks during 1956-86 was found to be 22 per cent. This increase was also corroborated by the increase in the rice area during the above period in the district since these soils are used mainly for rice cultivation. During 1972-86, an increase in the extent of salt-affected soils on the periphery of large blocks was also observed, which was limited to 3 per cent.