"Soils of Tamil Nadu In Tamil Nadu, soils are classified into six orders, 12 sub-orders, 20 major groups, 44 subgroups and 94 soil families in the hierarchy. As per the USDA system of soil classification (Taxonomy), the soils of Tamil Nadu are classified into six orders viz, Entisols, Inceptisols, Alfisols, Mollisols, Ultisols, Vertisols. Inceptisols cover about 50% of the state’s total geographical area followed by Alfisols (30%), Vertisols (7%), Entisols (6%), Ultisols (1%)and negligible area by Mollisols. About 5% of the area is miscellaneous land types, which include rocklands, marshes, urban areas and water bodies (Environmental Report; 2005, Dept. of Environment, Govt. of Tamil Nadu). Tamil Nadu has been covered by red sandy soils and red loamy soils, deltaic alluvial soils, black soils, laterite soils, mixed red and black soils, coastal alluvial soils. Red sandy soils and red loamy soils belong to the order of Alfisols. Deltaic alluvial soils belong to the order of Entisols; laterite soils belong to the order of ultisols and Oxisols; black soils mostly belong to the order of Vertisols. Coastal alluvial soils belong to the order of Entisols. Soils belonging to orders of Alfisols, Entisols, Vertisols, Inceptisols and ultisols cover 58600, 35600, 24400 and 12645 square kilometres respectively. Table and Figure exhibits the various soil orders and their distribution in Tamil Nadu.Source: Administrative Atlas of Tamil NaduOrders of the Soils Order Major Soils District(s) Coimbatore, Erode, Kancheepuram, Kanniyakumari, Namakkal, Nilgiris, Perambalur, Pudukkottai, Salem, ENTISOLS Sivaganga, Thiruvarur, Thiruvallur, /INCEPTISOLS Alluvial soil Tiruvannamalai and Viluppuram Kanniyakumari, Tirunelveli and ENTISOLS Coastal Alluvium Tiruvannamalai ENTISOLS River Alluvium Kanniyakumari, Karur and Tiruvannamalai ALFISOLS Red calcareous soil Coimbatore and Erode Red non calcareous ALFISOLS soil Coimbatore and Erode Dharmapuri, Kancheepuram, Karur and ALFISOLS Red loamy soil Perambalur ALFISOLS Red Sandy Soil Dindigul, the Nilgiris and Virudhunagar ALFISOLS Red Ferruginous soil Cuddalore and Ramanathapuram Coimbatore, Cuddalore, Dharmapuri, Dindigul, Erode, Krishnagiri, Madurai, Nagapattinam, Namakkal, Nilgiris, Perambalur, Pudukkottai, Ramanathapuram, Salem, Sivaganga, Theni, Thoothukkudi, Tirunelveli, Thiruvallur, Tiruvannamalai, Tiruchchirappalli, Vellore, Viluppuram and VERTISOLS Black soil Virudhunagar ULTISOLS Kanniyakumari, Sivaganga and /OXISOLS Lateritic soil Tiruvannamalai Source: Statistical Handbook of Tamil Nadu Order Alfisols Red sandy soils and red loamy soils have covered the major area of Tamil Nadu. Acidic parent materials like granite, gneiss, quartzite, sandstone etc. are weathered to form the red sandy soils and red loamy soils. Red coloured haematite or yellow coloured limonite have closely adhered with sand particles to impart various shades of red and yellow colour to these soils which usuallycontain ferruginous gravels consisting of iron, aluminium and silica. These sandy, loamy sand and sandy loam soils are leached systematically enough to impoverish them of basic elements and plant nutrients. The soil particles are coated with ferric oxide (Fe O ). So soils are red in colour; 2 3 calcium is an important exchangeable cation in them to make them neutral to slightly alkaline in reaction. Soils formed from the weathering of Cuddalore sand stone are of loamy texture, deep to light red, yellow and light yellow in colours are low in humus, nitrogen and phosphorus. The soils are poor cation exchange capacity found only in a small area at the western side of Badalur. Brownish grey loam or clay rests as the top layer of one foot thickness; the sub-soil is brown and becomes sandy below the top layer up to three feet. Soils are very hard at the surface and the sub surface, poor in humus and high in potash with a poor in cation exchange capacity and alkaline in reaction and do not contain soluble salts (Rajan, G. and Gopala Rao, 1978). The red soils of Tamil Nadu to possess above 18.2% clay, 6.1% silt, 23.6% fine sand, 6.0% ferric oxide (Fe O ), 1.5% alumina (Al O ), 11.7 (mille equivalent)meq/100gm soil 2 3 2 3 CEC (carbon exchange capacity), 93.2 PBS (phosphate buffered saline), 6.6 pH (power of hydrogen), 5.6 meq/100gm soil exchangeable calcium (CaCo3), 0.1% organic carbon (C), 85 ppm (parts per million)available in nitrogen (N), 12 ppm available in phosphorus (P) and 12.5 ppm water soluble potassium (K). (Manikam and Mosi, 1985) Manickam and Mosi (1985) have given the under-mentioned characteristics of the soil profile of the order of Alfisols.Depth (cm) Soil Characteristics 0-12 Sandy clay loam soil of Dark-red in colour 12-40 Sandy clay loam soil of Dark-red in colour 40-85 Sandy clay loam soil of Dark reddish-brown in colour 85 + Gravelly sandy clay Palathurai series of soils which are a member of fine loamy mixed isohyperthermic family of typic Haplustalfs. Calcic gneiss is weathered on the very gently sloping to undulating upper and middle pediments (interfluva plains)lying at 375 to 400 metres above the MSL under semi-arid tropical climate with a mean annual rainfall of 570mm and mean o annual temperature of 26.5 C. The spread of this soil is found in Coimbatore, Salem and Dharmapuri districts of Tamil Nadu where the mean annual temperature of the soil at its 50 o cm depth is 27.5 C and mean summer soil temperature differs from the mean winter soil o temperature by only 0.5 C (Lal et. al. 1994). The soil profile is as follows: A - horizon is 10 to 15 cm thick, reddish brown in colour, loamy sand to sandy loam in p texture containing lime concretions in various proportion. B - horizon is 40 to 60 cm thick, reddish brown and gravelly sandy clay loam to clay loam in t texture. Palathurai series soils are moderately to strongly alkaline in reaction with a low to medium water holding capacity and cation exchange capacity of 13 to 25 meq/100 gm soils. They are having a low to medium productivity potential suitable for the cultivation of Sorghum and horse gram.Order Entisols In this order alluvial soils are included. The deltaic alluvial soils are found in Thanjavur district. A belt of coastal alluvial soils extends from Chennai (Madras)to Kanniyakumari. Alluvial soils are most fertile in Tamil Nadu. These soils are thick and deep, and are constituted of sand, silt and clay in alternate layers of varying thickness. The surface soil is commonly of loamy texture. The Cauvery alluvial soil is poor in humus, nitrogen and phosphorus but rich in potassium and lime, and are having low cation exchange capacity with alkaline reaction. Depth (cm) Soil Characteristics 0-14 sandy loam in texture, Reddish-brown in colour. 14-33 sandy loam in texture, Reddish-brown in colour. 33-82 sandy loam in texture, Reddish-brown in colour. 82-115 sandy clay loam in texture, Dark Reddish-gray in colour. 115-143 + loamy sand in texture, Dark Reddish-brown in colour. Coastal alluvial soils develop on recent marine deposits. They display the influence of the sea which is indicated by the occurrence of shells and bleached sand. They are also constituted by sand, silt and clay in alternate layers and are poor in nitrogen and phosphorus and are rich in potassium and lime. Salts also occur in some of them. (Rajan, G and Rao, G., 1978) Described below is the profile of the soil which belongs to the order of Entisols as have been reported by Manikam and Mosi (1985).A - horizon is 10 to 15 cm thick, reddish brown in colour, loamy sand to sandy loam in p texture. B - horizon is 40 to 60 cm thick, dark reddish brown and gravelly sandy clay loam to clay t loam in texture. Alluvial soils with sandy clay loam texture possess 34.3% clay, 15.8% silt, 19.6% sand , 3.5% ferric oxide (Fe O ), 5.0% alumina (Al O ), 16.9 meq/100 gm soil cation 2 3 2 3 exchange capacity, 22.8 meq/100 gm soil exchangeable calcium, 94.7 % base saturation, 0.6 % organic carbon, 119.9 ppm available nitrogen (N), 35 ppmavailable phosphorus (P) and 10 ppm water soluble potassium (K). Order Vertisols In this category of soils black soil are included. The black soil profiles of Tamil Nadu are shallow with a thickness of the layers varying from 0.9 to 1.2 metres, and a depth of 2.7 metres or more. Both kinds of black soil profiles may or may not possess gypsum. Hard kankar layer occurs in the shallow black soils at about 46 to 61 cm depth overlying partially weathered parent rocks. Black soils contain 65% to 85 % clay and 5% to 7 % lime (CaCO ). 3 They are slowly permeable. Their hygroscopic coefficient, pore space percentage, water holding capacity and particle density are high. They are deficient in nitrogen but possess enough phosphate (PO ) and potash (KO). (Raychaudhury and Rajan, G, 1971) 2 5 2 Manickam and Mosi (1985)have given the following characteristics of black soils of Tamil Nadu.Depth (cm) Soil Characteristics 0-17 Clay in texture, Very Dark-grey in colour 17-49 Clay in texture, Very Dark-grey in colour 49-80 Clay in texture, Very Dark-grey in colour 80-125 Clay in texture, Very Dark-grey in colour 125 + Clay in texture, horizon is variegated in colour According to Manickam and Mosi (1985), black soils of Tamil Nadu of Vertisols order with a sandy clay in texture posses 35.5 % clay, 13.8% silt19.6% sand, 3.9% ferric oxide (Fe O ), 12.2% alumina (Al O ), 54.2 meq/100gm soil cation exchange capacity, 22.8 2 3 2 3 meq/100 gm soil exchangeable calcium, 1.1% calcium carbonate, 94.3 % of base saturation, 0.3% organic carbon, 48 ppm available nitrogen (N), 10 ppm available in phosphorus(P)and 9 ppm water soluble potassium (K). The medium black soils are belonging to Kalathur series that is a member of fine montmorillonitic isohyperthermic family of Udorthentic Pellusterts. These soils have been found in the Cauvery delta in Thanjavur district of Tamil Nadu. They have been developed in the Cauvery deltaic alluvium on nearly level to very gentle slope under semiarid tropical o climate with mean annual rainfall of 870mm and mean annual temperature of 26.8 C. Mean o annual soil temperature is 27.8 C. Mean summer soil temperature differs from mean winter o soil temperature by 3.3 C. (Lal, et. al., 1994) The soil column is 80 to 100 cm thick of profile as follows: A - horizon is 80 to 100 cm thick, dark grey in colour, very strongly alkaline in reaction, with lime concretion strong sub angular blocky and angular blocky structure and intersecting slickenside in the lower part of horizon 'A'. C - horizon is dark greyish brown in colour, clayey in texture and very strongly alkaline in reaction.Kalathur series soils are moderately well drained, and moderately alkaline in reaction of high water holding capacity and of high cation exchange capacity. Their productivity potential is medium to high. Paddy, Bengal gram, Black gram etc. are commonly grown on them. Order Inceptisols Manikam and Mosi (1985)have reported that soils belonging to the order of Inceptisols possess an Ochric epipedon and a cambic horizon as mentioned below. Soil depth (cm) Characteristics 0-11 Sandy loam in texture, Yellowish-red in colour. Nov-26 Clay loam in texture, Dark-red in colour. 26-48 Clay loam in texture, Yellowish-red in colour. 48 + Gneiss. Sohan Lal et al (1994)have described the soil which belongs to the Coimbatore series that is a member of fine montmorillonitic isohyperthermic family of Vertic ustropepts; sub- order Tropepts, order of Inceptisols. Fine textured alluvium of calcic gneiss has been transformed to the soil of Coimbatore series on level to very gently sloping inter-fluvial plains at 375 to 400 MSL. These soils receive mean annual rainfall of 570 mm in a semi arid o climate when mean annual temperature is about 26.5 C and are spread over Coimbatore o district of Tamil Nadu. The mean annual soil temperature is 27.5 C and mean summer soils o temperature is higher by 0.5 C only. The soil profile is as follows:A - horizon is 10 to 20 cm thick, greyish brown to very dark greyish brown in colour, clayey loam to clay in texture with lime concretion. B - horizon is 25 to 35 cm thick, very dark greyish brown to dark yellowish brown in colour, 3 clayey in texture with lime concretion. Coimbatore series soils are of imperfectly drained of clayey nature with medium to high water holding capacity and a cation exchange capacity of 38 to 50 meq/100 gm soils. These soils possess medium productivity potential where cotton, sorghum and pigeon pea are grown under unirrigated condition. Order Ultisols Raychaudhury and Govinda Rajan (1971) have said that laterite soils of Tamil Nadu are of in situ sedentary formations and are found in high rainfall areas. Rajan, G., and Rao, G. (1978)have reported that laterite soils occur in Kancheepuram, Thiruvallur and Thanjavur districts. They had been formed from varieties of parent material in humid climate. They are strongly acidic in reaction and rich in humus contents. Manickam and Mose (1985)have found them consisting of 43.6 % clay, 5.6 % silt, 19 % fine sand, 10.6 % ferric oxide (Fe O ), 2 3 15.4 % alumina (Al O ), 8.5 meq/100 gm cation exchange capacity, 3.9 meq/100 gm soil 2 3 exchangeable calcium, 2.3 % organic carbon, 136 ppm available nitrogen, 25ppm available phosphorus (P), 50 ppmwater soluble potassium (K) and 65.6 % of base saturation. Soil Depth (mm) Characteristics 0-8 Clayey in texture, Reddish black in colour 8-18 Clayey in texture, Very dark brown in colour 18-68 Clayey in texture, reddish brown in colour 68+ Clayey in texture, yellowish red in colour"