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 Symposium Series No.2, 2009)

Abstract

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).