Influence of soil organic carbon, water holding capacity and moisture content on heavy metals in rice paddy soils of Western Ghats of India

Analysis of soil samples collected from 16 rice paddy fields located in Western Ghats region was made to quantify the heavy metals concentration. Heavy metal analysis was done for Cu, Zn, Mn, Fe, Ni, Cr, Cd, and Pb using atomic absorption spectroscopy. High concentration of these heavy metals was found in rice paddy fields regularly being cultivated using agrochemicals. We compared this concentration with soils of rice paddy field that was not under cultivation. Cu, Zn, Mn, Fe, Cr, Ni, Pb, and Cd showed a build up at an order of 1.2, 1.3, 2.3, 2.2, 1.8, 2.8, 1.8, and 8.5 times higher in the rice paddy fields cultivated with agrochemical applications. Heavy metals exhibited maximum association (PCA) with soil moisture content (Zn, Fe, Cr, Ni, and Cd), organic carbon content (Fe, Cr, Ni, and Cd) and water holding capacity (Cu, Pb, and Cd). Such associations were absent in the reference site. This indicates the build-up of heavy metals in rice paddy soils under the strong influence of moisture content, water holding capacity, and organic carbon content of the soil.