National highway induced selected chemical properties of soils across tea bowl of India: scale and assessment.

Abstract

National Highway may have damaging effect on soil chemical properties. In this study, a scale and assessment of selected chemical properties of tea growing soils with increasing sampling distance from National Highway have been documented. Top and sub soils from ten tea estates surrounding the National Highway of Dibrugrah and Tinsukia districts at the Upper Brahmaputra plain of India were analysed to understand the variation of the selected chemical properties influenced by National Highway. Significantly lower (p < 0.05) pHs and higher electrical conductivity were found in top soils than sub soils irrespective of sampling location from National Highway reflecting higher amount of soluble salt in top soils. Organic carbon (7.52–25.88 g kg−1), total nitrogen (0.70–2.47 g kg−1), available phosphorous (14.11–28.82 mg kg−1) and potassium (95.24–125.92 mg kg−1) were found significantly higher (p < 0.05) in top soils than sub soils irrespective of sampling locations. Total concentrations (g kg−1) of copper (0.012–0.034), iron (17.62–35.25), manganese (0.057–0.448) and zinc (0.039–0.097) in top soil were higher than the sub soil (copper: 0.012–0.029; iron: 15.57–31.15; manganese: 0.053–0.340 and zinc: 0.038–0.074). All the soils samples were found non-contaminated according to Indian standard. Application of generalized linear model revealed significant differences in metal content across the sampling distances from the National Highway. The novelty of this study is that tea growing soils in this region characterized by traffic-related build-up metals in top soils near to National Highway. Hierarchical cluster analysis and principal component analysis were applied to form homogenous groups of the studied parameters.