石灰系下水汚泥連用中止後の土壌pH低下に伴う重金属類の存在形態, 移動性および可給性の変化

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Changes in form, mobility and availability of heavy metals (Ni, Cu, Zn and Cd) were observed after soil amendment with limed sewage sludge was terminated. Soil plots which had received annual rates of 0,1,2 and 4 kg m^<-2> of sewage sludge between 1979 and 1985 (total of 0,7,14 and 28 kg m^<-2> sludge for 7 y) were then planted annually with spinach (spring) and cabbage (autumn) between 1986 and 1989 (total of 8 crops). The acid fertilizer, ammonium sulfate, was incorporated into the soils at the rate of nitrogen 94 g m^<-2> before the start of each crop. During the years of sludge applications, increasing soil pH, due to the large amount of calcium hydroxide present in the sludge, decreased the mobility and plant availability of the heavy metals. The chemical forms of these metals were present mostly in the carbonate and Fe-Mn oxide fractions. During the years of ammonium sulfate application, the pH in the soil plots decreased and the metals changed to easily exchangeable forms, thereby accelerating their mobilization and plant uptake. On the basis of these results, it appears that the optimum amount of sewage sludge application should be less than 1 kg m^<-2> a year. This rate is similar to that used for organic matter application in Japan, and should maintain soil pH in the range of 6.3 to 6.8
2001-02-05