Soil Fertility Constraint Assessment Using Spatial Nutrient Map at Three Selected Villages of Coastal Sundarbans Tarik Mitran* 1 , Pabitra Kumar Mani 1 , Nirmalendu Basak 1 , Biswapati Mandal 1 and Subrata Kumar Mukhopadhyay 2 1 Directorate of Research, Bidhan Chandra Krishi Viswavidyalaya, Kalyani-741 252, Nadia, West Bengal, India 2 National Bureau of Soil Survey and Land Use Planning (NBSS&LUP), Kolkata-700 091, West Bengal, India *Email: tarik.bckv@gmail.com Abstract Soil fertility constrains were studied in three representative villages i.e. Tushkhali, Duchnikhali and Korakati with collecting and interpreting a large number of geo-referenced soil samples of Sundarbans. The Global Positioning System (GPS) based soil reaction, salinity and nutrient maps were prepared by Inverse Distance Weighted (IDW) spatial interpolation method using ArcGIS Ver. 10 software. Soils were mostly heavy in texture (clay > 50%), highly acidic to neutral in reaction and associated with marginal salinity. Although an extreme acidity (< 4.8) or higher salinity level > 4.0 dS m -1 was detected in some of the pockets. Among the three villages, Tushkhali showed comparatively higher electrical conductivity (EC) with highest value of 5.23 dS m -1 . There was a decreasing trend in EC recorded with higher level of organic C with irrespective of sampling sites. On an average, organic C of the studied area was medium to high in nature. Soils were poor in available nitrogen and medium to low in available P and Zn. Higher availability status of K, Mn, Cu, Fe and S were found in such soils. Nutrient Index values for all the studied plant nutrients were generated. These values revealed that area is poor in available N; medium in available P and Zn but the native supply of available K, S and micronutrients are in much pronounced. The available N, P and Zn contents significantly increased with increase in organic C of soil. Key words: Acid soil, ArcGIS, Salinity, Soil fertility, Spatial nutrient map, Sundarbans Introduction Coastal regions, home to a large and growing proportion of the world’s population, are undergoing environmental decline. The problem is particularly acute in developing countries. The reasons for environmental decline are complex, but population factors play a significant role. Today, approximately 3 billion people- about half of the world’s population live within 200 kilometres of a coastline. By 2025, figure is likely to be double. The Coastal agro-ecosystem occupies vast area of land in India. About 20% of the population of India lives in coastal areas. In coastal areas of India, salt affected soils stand to be one major challenge in preventing agricultural activities. On global basis salt affected soils occupy an estimated area of 952 million ha, nearly 7% of total land area or approximately 33% of the potential arable land area of the world (Szabolcs, 1979). In India, out of an estimated area of 187.7 million hectares of total degraded land, 9.38 million hectares are salt affected soil (Dagar, 2005) and out of which 3.1 million hectares are in the coastal region (Yadav et al., 1983). Among the states in India, West Bengal has the largest area (0.82 million hectares) of the salt affected soils in the coastal region, between 87º25' E and 89º.0' E latitude and longitude 21º30' N and 23º15' N covering the district of North and South 24-Parganas, Howrah and East Midnapore. The great Sundarbans, the delta region of the river Ganges, occur in the coastal tracts of North and South 24-Parganas constitute a major portion of coastal region of India with wide variability in climatic, topographical and edaphic conditions. The climate is typical tropical with wide variation in the annual rainfall from 300-3000 mm. The rainfall is mainly concentrated during the South-West monsoon from June to September when more than 80% of the rainfall is experienced in the region. The rainfall in the rest of the period of the year is meagre. Beside that the entire area of Sundarbans faces the problem of salinity, waterlogging and drainage congestion. In the absence of upland water supply the area is exposed to tidal action making the water highly brackish. The soil salinity shows wide spatial and seasonal variability, being minimum in the monsoon season and maximum in the summer season (Bandyopadhyay et al., 2001). The degraded soil and water Journal of Soil Salinity and Water Quality 6(1), 1-8, 2014 *Corresponding author, Present address: Soil and Land Resources Assessment Division, Land Resources, Land use Mapping and Monitoring Group, National Remote Sensing Centre, Hyderabad, India