Characterization of Sodic Soils of North Western Zone of Tamil Nadu

An attempt has been made on characterization of sodic soils by using reconnaissance soil survey methods in North Western Zone of Tamil Nadu encompassing the districts of Dharmapuri, Salem, Krishnagiri and Namakkal during January 2009 to August 2009. Surface soil samples were collected as per reconnaissance soil survey reports of Dept. of Agriculture and analyzed the soil pH and EC. Based on the analytical report the severity of sodicity problem was quantified. Then profiles were dug and detailed analyses were taken up in the sodic soil inflicted areas. Considerable area of sodic soils to the extent of 26,279 ha was identified under the soil series viz., Peelamedu, Salem, Mallur, Thulukkanur, Mallasamudram, Upparapatti, Periyanaickanpalayam, Nattam, Dharmapuri, Krishnagiri and Harur. Among the soil series detailed analysis of profile samples like pH, EC, ESP and SAR the Mallasamudram soil series was identified as most affected by sodicity. The pH range of the above series was 9.1 to 10.0, EC of 0.8 to 1.2 dsm -1 and ESP of 32 and 48 per cent was predominantly noticed compared to other soil series. The land capability and productivity classes were poor in the above soil series.

The present population of the country is 1110 million and the annual food grain production has been to a tune of 205 million tonnes. India's population is expected to cross 1400 million by 2025 A.D. With this scenario in mind, on an average, the country has to raise the annual food production by 5 million tonnes from the existing 205 million tonnes to reach the food grain requirement 261.5 to 267.0 million tons by 2020-2021 (Chand, 2007). In order to cope with the food grain requirements of the increasing population, the agricultural production has to be stepped up substantially. This can be done either by multiple cropping on the existing cultivated lands or by bringing the additional land area under cultivation. The possibility to increase the food grain production to the required extent by these two ways is very much limited in India. The only feasible alternative is to increase the cultivated land area by bringing the wastelands and problem soils under cultivation.
The problems of soil sodicity, salinity and of poor quality water are likely to increase in the near future due to planned expansion in irrigated area and intensive use of natural resources to meet food, fodder, fibre and timber requirement of the burgeoning human and livestock populations. Tentative estimate indicates that the salt affected soils will constitute nearly 13 m ha area in the country by 2025. Out of this, Tamil Nadu State alone has 0.43 million ha of salt affected soils. The reclamation and utilization of thirteen million hectare of salt affected soils can lead to an additional production of 50 -60 million tonnes of food grain every year. As a result of the technologies generated by the CSSRI, Karnal over the years, more than 1.3 million ha salt affected soils have been reclaimed. The reclaimed area is contributing more than 8 million tonnes additional food grains (Anon., 2007).
The study area encompasses the districts of Dharmapuri, Krishnagiri, Salem and Namakkal which comes under the North Western Agro Climatic Zone of Tamil Nadu. The Agro Climatic Zone is the ideal and common working unit of all agricultural developmental activities; considerable area of sodicity in this zone hampered the agricultural production. The reclamation of these area leads to increased productivity and hence, the present study was under taken covering a specific zone.

Soil characterization
Soil Survey and Land Use Organization of the State Department of Agriculture, Government of Tamil Nadu generated soil maps for the study area, comprising the districts of Salem, Namakkal, Dharmapuri and Krishnagiri. They were utilized as the basic data in the present study. Further a detailed reconnaissance soil study was carried out in the villages where soils are affected by sodicity as per procedures outlined in the USDA Soil Survey Manual *Corresponding author email: agrokumar@yahoo.com (1999) using village cadastral maps. Taking into consideration of the nature of soil series, intensive field surface samplings (0-15 cm) were taken up in sodic soil affected villages. Sampling intensity was based on the rate of soil inflicted with sodicity. These surface soils were analyzed for its pH, EC (potentiometry- Jackson, 1973), and identified village wise sodicity inflicted area. For the characterization of soils, systematic field traverse were made, profiles examined and horizon wise samples were collected (USDA, 1999). Based on the analytical results, taluk wise salt inflicted area have been identified and tabulated.

Results and Discussion
Based on the surface soil samples analytical results, taluk wise salt inflicted areas have been identified and tabulated ( Nattam, Dharmapuri, Krishnagiri and Harur series are found to be inflicted with the problem of sodicity in patches excepting Mallasamudram series. The results of profile soil sample analysis are given in Table 4. The soil analytical results revealed that the samples collected from Tiruchengode and Sankari taluks, which are adjacent to each other, recorded higher pH range compared to others taluks. Next to this, Krishnagiri taluk recorded higher number of samples under the pH range of 9-10. The occurrence of Mallasamudram soil series both in Sankari taluk of Salem district and Tiruchengode taluk of Namakkal district extends to an area of 4228 ha. Analytical results of surface soil samples revealed that, the above soil series are highly sodic and contiguous.

Problem soils of ayacut areas
North Western Zone has dams constructed for irrigation purposes in Krishnagiri district. Krishnagiri Reservoir Project (KRP) irrigates around 3600 ha. The irrigated areas are nearly level in topography and the distributory system of unlined canals leading to seepage and water logging. It is estimated that 2000 ha of KRP dam ayacut area was affected by varying magnitude of sodicity. The problem soil series like Nattam, Krishnagiri and Thimmapuram revealed that the surface soil texture was found to be clay loam and is heavy in nature due to which the drainage is the problem. In Salem district the total ayacut area of Mettur dam is 6050 ha out of which 966 ha of Tulukkanur, Upparapatti soil series were found to be affected by sodicity. With regard to Namakkal district, out of total Mettur dam ayacut area of 4528 ha, an area of 882 ha in Pallipalayam and Upparapatti soil series were found to be affected by varying degree of sodicity. The problem of soil sodicity is due to inadequate drainage and unlined canals.

Problem soils of non-ayacut area
In North Western Zone of Tamil Nadu, Tiruchengode taluk of Namakkal district was most affected by sodicity with an area of 3802 ha; the major soil series affected being Mallasamudram and Sankari taluk of Salem district being affected by sodicity with an area of 3498 ha, the major soil series affected being Mallasamudram. Among the soil series studied Mallasamudram soil series is found to be more sodic with a pH range of 9.0 to 10.0. Among different soil series profile, detailed analysis

Table 2. Details of taluk wise and soil series wise sodic soil area (in ha)
District Taluk  Sodic soil occurring soil series  Plm  Slm  Mal  Tlk  Msm  Upi  Pyk  Total   Salem  Salem  232  544  388  30  23  --1217  Vazhapadi  35  551  303  ----889  Sankari  ---836  2212  450  -3498  Omalur  500  ------600  Mettur  200  ------170  Attur  ------2731  2731  Total  967  1095  691  866  2235  450  2731  showed that profile samples of Mallasamudram soil series recorded higher pH and ESP. The texture of the above soil series is also clay loam in nature. Similar findings were reported by Venkatesan and Thiyagarajan (1998) and Anon (2001). The available Table 3. Details of profile soil sample analytical result nutrient status of these soils indicated that N was low, P and K are low to medium respectively. In general, salt affected soils are low in N status owing to poor organic matter content, slower rate of its transformation and mineralization and increased  Malival and Timbadia, (1993). Available micronutrient status of the study area soils indicated that Zn was deficient in both the locations. High pH, low organic matter content and high CaCO3 strongly limit the micronutrient availability particularly Zn and Cu to the crops. Similar findings were reported by Singaravel (1997).

Profile analysis
In general, the profile depth of problem soils like Mallasamudram, Upparapatti, Periyanaickanpalayam, Nattam, Krishnagiri and Harur are deep in soil depth. The texture varied from clay loam to clay. It showed that the problem soils are heavy textured and the permeability is very slow.
The results of profile analysis confirm that the higher pH leads to sodicity. The CEC value also correlated with heavy texture. The values of exchangeable Na and ESP confirm the sodicity in soils. Due to poor drainage, sodicity and heavy texture the problem soils come under LCC class of II and III (Tables 3 and 4).