85 N Save Nature to Survive 8(1&2): 85-89, 2014 www.theecoscan.in FORMS OF SULPHUR AND THEIR RELATIONSHIP IN FOUR CONTRASTING AGRO-CLIMATIC ZONES OF WEST BENGAL, INDIA BAPPA PARAMANIK 1 , PARIMAL PANDA 1 , JAYANTA LAYEK 2 , DIBYENDU CHATTERJEE 3 * AND ASHOK CHOUDHURY 1 1 Department of Soil Science and Agricultural Chemistry, Uttar Banga Krishi Viswavidyalaya, Pundibari, Cooch Behar, West Bengal - 736 165, INDIA 2 ICAR Research Complex for NEH Region, Umiam, Meghalaya - 793 103, INDIA 3 ICAR Research Complex for NEH Region, Nagaland Centre, Jharnapani, Medziphema, Nagaland - 797 106, INDIA e-mail: dibyenducha@gmail.com INTRODUCTION Sulphur (S) is one of the 17 nutrient elements essential for growth and development of all plants. It is the thirteenth most abundant element in the earth crust with an average concentration of 0.06%. It is now considered as the 4 th major plant nutrient after nitrogen (N), phosphorous (P) and potassium (K) (Patel et al., 2013a). It resembles N in its role and function in plant production, is comparable to P in terms of overall crop needs and could be equated with K in terms of per unit cost. Sulphur containing amino acids like cystine, cysteine and methionine and promotes nodulation in legumes (Patel et al., 2013b). The yield attributing characters of crops were greatly affected by sulphur application (Choudhary et al., 2014). Sulphur is one of the constituents of essential oils, imparting flavour, and sharpness in onion, garlic etc. (Havlin et al., 2004). It is present in soil both in organic and inorganic forms like sulphate (SO 4 -2 ) and sulphide (S -2 ) but is primarily taken up by plants as the SO 4 -2 ion. The common forms of inorganic sulphur in soils are (1) water soluble sulphate (2) adsorbed sulphate (3) insoluble sulphates of Ca, Ba, Fe etc. and (4) sulphides or other reduced forms of sulphur. Sulphate is present in soil either water-soluble or adsorbed form; the latter depends on soil characteristics such as content of iron oxide/hydroxide and pH. Much of the organic sulphur in soils remains uncharacterized and three broad groups of sulphur compounds are recognized. They are (1) HI-reducible sulphur (2) C-bonded sulphur and (3) residual or inert sulphur. Organic sulphur is a reserve source of sulphur for plants and must undergo mineralization before it becomes available to plants. As sulphur immobilization is microbial process, it depends on factors like moisture, aeration; temperature soil reaction etc. Organic sulphur of the soil has been designated as indicator of reserve sulphur status of soil (Kumar and Singh, 1974). Non-sulphate inorganic fraction of sulphur is attributable to (1) primary minerals (2) pyrites or iron polysulphides formed as a result of water logging (3) insoluble barium or strontium salts and (4) co-crystallized impurities in calcium carbonate. Appreciable amounts of soluble sulphates are often found in subsoil horizons and the occurrence of free gypsum in the deeper horizons of many semi-arid soils is a well-known pedological phenomenon. Several forms of insoluble sulphates such as Ca, Ba and Sr, are associated with basic sulphates of Al, Fe and calcium carbonate. The amount of total sulphur present in soils vary depending upon its content in the primary material, organic compounds and sulphate ions adsorbed and present in the soil solution. It occurs largely in organic form in humid and sub-humid soils and in inorganic forms in arid and semi-arid regions with low rainfall where salt accumulation is high. Received : 19.12.2013 Revised : 12.04.2014 Accepted : 16.05.2014 *Corresponding author KEY WORDS Agro-climatic regions Correlation Forms of sulphur ABSTRACT To study different forms of sulphur and their relationship in four contrasting agro-climatic zones of West Bengal (hill, terai, new alluvial and old alluvial), soil samples were collected from different districts of West Bengal (Darjeeling, Cooch Behar, Murshidabad, Dakshin Dinajpur, Malda, and Uttar Dinajpur) to analyze the different forms of sulphur viz. available S, total S, organic S, sulphate S (SO 4 - S), heat soluble- S, water soluble-S, adsorbed S and non-sulphate S). Soils were also analyzed for several physico-chemical properties and amorphous constituents following the standard laboratory procedures. The result showed that, available nitrogen content were very low in hill (66.12 to 75.25 kg/ha) as compared to new alluvial (324.89 to 487.96 kg ha -1 ). Hill region recorded the highest phosphorus content (76.34 to 88.86 kg ha -1 ) while terai recorded the lowest (11.08 to 11.54 kg ha -1 ). The available potassium content in soils was ranged between low to medium across the region and samples. Available sulphur content of the soils varied from 16.85- 38.23 mg kg -1 , whereas total sulphur varied from 265.30 -460.15 mg kg -1 . Available sulphur had significant and positive correlation with total sulphur (0.516), sulphate sulphu (0.514), heat soluble sulphur (0.766), and adsorbed sulphur content (0.693). Total sulphur showed significant and positive correlation with all form