Salinity appraisal using IRS images in Shorapur Taluka, Upper Krishna Irrigation Project, Phase I, Gulbarga District, Karnataka, India

Abstract

Shorapur Taluka, located between 76°15′ and 76°56′ E longitudes and 16°10′ and 16°35′ N latitudes, was the first area to receive irrigation waters from the Krishna left bank canal under the Upper Krishna Irrigation Project in the district of Gulbarga, in the state of Karnataka, India. The soils in Shorapur are extensively affected by the problems of salinity and water logging. Images from IRS ID LISS‐III for 27 March 1999 were interpreted to assess the extent to which salt‐affected soils could be identified and inventoried and mapped. It was found that salinization occurs especially in the valleys and on lower slopes as well as on side slopes of the low granitic hills covered with red soils. Electrical conductivity (EC) and pH could not be related to the DN values on the images and therefore into mapping classes due to the wide variation in the field. Using an accuracy assessment carried out to assess the supervised classification it was possible to identify the severely affected saline‐alkali soils with the greatest accuracy (85% accuracy). Severely affected alkali soils could be identified with 52% accuracy. The other classes identified were not significantly accurate. Based on image characteristics and ground data, salt‐affected soils were designated with classes based on severity as moderately affected, severely to moderately affected, and severely affected in terms of area affected as under <40% affected, 40–75% affected and >75% affected and the brightness on the imagery. The total salt‐affected area surveyed was 21 094 ha, of which severely salt‐affected lands were 33%, severely to moderately affected were 40%, and moderately affected were 27%, respectively and belong to the great groups Sodic Calciusterts, Halic Calciusterts, Aquic Haplustepts, Sodic Haplusterts, Typic Haplusterts and Fluventic Haplusterts. The total area covered and surveyed was approximately 0.12 million ha..

Acknowledgements

The team is grateful to the Indo‐Dutch Network project for providing the infrastructure and finance for data acquisition as well as travel and fieldwork. We wish to thank the two anonymous reviewers for their suggestions. We thank Mr Kashmir Singh and the staff at Bheemarayangudi, Gulbarga District, Karnataka for help with the collection and processing of the soil samples and soil analysis. We are grateful to the farmers who guided our path in remote inhospitable areas.