Saturday, 15 July 2006

Influence of Soil Characteristics on Profile Distribution of Trace Elements in Indo-Gangetic Alluvial Plain of India.

Kuldeep Singh, Dept of Soil Science, CCS Haryana Agricultural Univ, Hisar-125004, India

Soil acts as a sink and is the primary recipient of global emissions of trace elements which are either essential or potentially toxic to plants, animals or humans. Trace elements are elements that are generally present in relatively low concentration in soils or plants. Monitoring of trace elements in soils and a better understanding of factors influencing their variability are important to control animal and human exposure via food. Soil trace elements have both natural and anthropogenic sources. The availability of trace elements is affected by a combination of factors and the share of each factor would be known only by working multiple regression analysis with the available trace element as the dependent variable. Therefore, prediction values comprising different variables were arrived at in the present study of profile distribution of trace elements as influenced by soil characteristics. Ten representative soil profiles were exposed to cover the alluvial plain of Haryana State which forms a part of the vast Indo-Gangetic alluvial plain of Northern India. After processing the soil samples were analyzed for relevant soil properties and concentrations of trace elements were measured in 0.005 M DTPA extractable solution by AAS. Correlation and regression analyses were carried out. The different soil characteristics vary widely in the soil profiles. The clay content (4.0-32.0%) generally increased in subsurface horizons compared with surface. The pH of the soils was neutral to alkaline (6.5-8.6) and soluble salts were 0.31-9.90 dSm-1. Organic carbon was generally low (0.05-0.68%, average 0.23%). Calcium carbonate was in traces except in some layers of few profiles. The cation-exchange capacity was 1.3 to 9.8 with a mean value of 4.6 meq/100g. This soil profiles revealed a high horizontal and vertical variability of the distribution of trace elements. The DTPA extractable Pb, Cd, Cr, Co and Ni ranged from 0.71 to 8.01, 0.05 to 0.48, 0.02-0.08, 0.43 to 3.53 and 0.04 to 1.51 mg kg-1, respectively. In different pedons, the amount of Zn, Cu, Mn and Fe extracted by DTPA ranged from 0.34 to 1.89, 0.20 to 5.88, 13.46 to 39.83 and 11.20-71.44 mg kg-1, respectively. The order of extractabilty of mean values was Mn > Fe > Pb > Co > Cu > Zn > Ni > Cd > Cr. The results showed that trace elements content in surface strata decreased with increasing depth. Relatively less amount of trace elements at lower depth was due to the restricted mobility of the elements into the lower horizons. Multiple-regression analysis showed that the four soil characteristics together accounted for 44, 31, 13, 43, 60, 70, 61, 55 and 63% variation in the availability of Pb, Cd, Cr, Co, Ni, Zn, Cu, Mn and Fe, respectively. From the comparative study of partial regression coefficients it was found that organic carbon content was the dominant soil factor which showed significant influence on the distribution of all the nine trace elements. There is no existing deficiency of essential micronutrients and potential adverse impact of contamination by heavy metals in the present studied soils.

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