Computerized database of salt affected soils for Peninsular India using GIS

Abstract

A computerized database of salt affected soils was prepared for five states – Andhra Pradesh, Karnataka, Tamil Nadu, Kerala and Orissa – based on the analogue maps of the National Remote Sensing Agency (NRSA), Hyderabad, India. The salt affected soil maps at 1:250,000 scale were georeferenced and digitized to prepare the digital polygons of salt affected soils using ILWIS software. The Survey of India State map at 1:1,000,000 scale was georeferenced and features for administrative and political boundaries (state/district), infrastructure (road/railway), irrigation and drainage (river/canal) and settlements (state/district capitals) were digitized to prepare the thematic layers for the basemap. These were overlaid onto the salt affected soil layer to prepare the state map of salt affected soils. A composite (master) database comprising salt affected soils in five states was prepared using GIS. The soil characteristics such as nature and degree of salinity/sodicity and its ground coverage were entered in an attribute table and linked with the digitized polygons to prepare a relational database. Four agroclimatic regions (ACRs) and 42 agroclimatic zones (ACZs) were identified by the Planning Commission of India for regional planning and development of natural resources in Peninsular India. The boundaries of the ACRs and ACZs were delineated from the primary (master) database using ILWIS GIS. Superimposing digitized boundaries of ACRs and ACZs over the master database, the salt affected soils were delineated to show the distribution of salt affected soils at regional and zonal scales. The state-, region- and zone-wise extent of salt affected soils was calculated. The soils were essentially saline in Orissa and Kerala state, distributed in the coastal, deltaic plains and mud flats/mangrove swamps. In Andhra Pradesh, soils were saline (53%) and sodic (47%), distributed in the peninsular (64%), coastal (24%) plains and mud flats/mangrove swamps (12%). The salt affected soils in Karnataka were primarily sodic (99%), located in the alluvial plain. In Tamil Nadu, soils were dominantly sodic (96%), distributed in the peninsular (95%) plain. Soils with variable salinity were also found in the coastal (74%) and deltaic (16%) plains and mudflats/mangrove swamps (10%) of Orissa and in the coastal plain (3%) of Tamil Nadu. A significant area under salt affected soils (69%) was found in ACR XI (East Coast Plains and Hills Region), distributed in Tamil Nadu (34%), Andhra Pradesh (19%) and Orissa (15%); followed by 26% in ACR X (Southern Plateau and Hills Region), located in Karnataka (16%), Andhra Pradesh ((9%) and Tamil Nadu (2%) and 5% in ACR XII (West Coast Plain and Ghat Region), comprising Kerala (2%) and Tamil Nadu (3%) States. The zonal distribution showed that the extent of salt affected soils was higher in the semiarid regions (rainfall <1000 mm) of Karnataka (84%), Tamil Nadu (93%) and Andhra Pradesh (64%). State maps of salt affected soils in digital format were overlaid with agroecosubregions, landforms, geology and rainfall data to show the relation between the extent of salt affected soils and the characteristics of agroregions, climatic parameters and the nature of parent materials. Thus the digitization of salt affected soil maps in GIS format provides a georeferenced, easy-to-access and retrieve, relational database comprising thematic and attribute information of salt affected soils at state, regional and zonal levels and facilitates overlay and map calculation of related data for planning and decision making in the reclamation and management of salt affected soils in Peninsular India and other similar regions.