Study of vegetation index, land use and irrigation scheduling efficiency as affected by soil salinity in different blocks of coastal West Bengal using remote sensing and GIS

Abstract

The coastal areas of West Bengal mostly suffer from high soil salinity. The principal crop cultivated in the area is rice. Assessment of soil salinity is a need to improve crop yield for the area. IRSP6 L3 satellite data for 12th April, 2013 was collected from National Remote Sensing Agency (NRSA). Survey of India (SOI) maps, land use map and soil salinity maps were also collected from related organizations and were the inputs in GIS. Satellite data was analyzed and a normalized difference vegetation index (NDVI) map was prepared. From the map, NDVI values for different features were obtained through GIS. The image was supervised maximum likelihood (MXL) classified to produce different land use classes. Soil EC values were correlated with NDVI index obtained from satellite data. Irrigation scheduling efficiency was computed in CROPWAT 8.0 for different soil series. Mainly three types of salinity were observed in the GIS map (>10 dS m-1, 5-10 dS m-1 and 2-5 dS m-1). The EC value for rice crop was 0.4-0.7 dS m-1 and corresponding NDVI value was 0.40-0.46. The bare soils were having low NDVI values (0.18-0.20) and relatively high EC values (0.81-2.0 dS m-1). NDVI value of uncultivated grassland was 0.35-0.40 and that of forest it was 0.46-0.55. The difference of EC values obtained in GIS map and different features might be due to determination in different seasons, dilution of EC due to irrigation and different site selection. The land use classes obtained in satellite image were rice, vegetables, urban, bare soil, fallow land and water body. Out of a total area of 26399 ha cultivated area was 7000 ha and non-cultivated area was 13000 ha. Irrigation scheduling efficiencies for vegetables were more for Gosaba series for all kinds of water applications. Sonakhali series performed 2nd to Gosaba, where as Tangrakhali and Nikarighata soils performed below the above two soils. In general, with an increase in EC value of soil, there was a decrease in NDVI values for agricultural lands. EC value of soil is better correlated with NDVI in uncultivated fields than cultivated ones.