Effects of Nitrogen Fertilizer, pH, and Electrical Conductivity on the Solubility of Cadmium in Soil Solution(<Special Issue>International Symposium: Challenges to Soil Degradation Towards Sustaining Life and Environment, Tokyo Metropolitan University Sym

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We investigated the effects of nitrogen fertilizer, pH, and electrical conductivity (EC) on cadmium (Cd) solubility in soil solution. Water extracts of soils with added urea as a nitrogen source (soil(+)N), as well as soils with no additional N source (soil(-)N), were obtained at various times over the course of a 60 day incubation period. The EC (W-EC), pH (W-pH), and concentrations of NO_3^- (W-NO_3^-), SO_4^<2-> (W-SO_4^<2->), Cl^- (W-Cl^-), and Cd (W-Cd) of the water extracts were analyzed. W-Cd and W-NO_3^- in soil(+)N rapidly increased between day 0 and day 7 and then slowly increased until the end of the incubation. Simultaneously, the pH decreased rapidly during the first 7 days and then decreased slowly. For soil(-)N, W-EC increased slowly and W-pH decreased slowly, and the rates of change were stable over the entire incubation period. Similar trends were observed for W-NO_3^-. These results indicate that the changes in EC and pH could be attributed to the nitrification of urea and soil organic matter, which in turn increased the W-Cd (i.e., increased Cd desorption from the soil). In addition, we carried out multiple linear regression analysis (n=30) of W-Cd, W-pH, and W-EC. This analysis indicated that the partial regression coefficients for W-pH and W-EC on W-Cd were -0.561 and 0.774, respectively, and that W-pH and W-EC together were sufficient to explain the solubility of Cd in the soil (R^2=0.851).
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