A LACK OF BACTERICIDAL EFFECT OF SUBSIDENCE-MITIGATING COPPER IN ORGANIC SOILS

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Abstract
Two poorly humified peat soils, containing 23 or 1207 ppm (wt/wt) Cu, and two well-humified muck soils with 151 or 1264 ppm Cu, obtained from 3-yr-old field experiments on simulated extravagant applications of Cu for mitigation of organic soil degradation and subsidence, were used in this study. The aim was to determine whether the longevity of Escherichia coli (K12 JE 2517-a nonmotile mutant) cells inoculated into the soils would be affected by the soil Cu concentrations. The rapid spread plate method was used for counting viable cells of the coliform. Both microbially active and bromomethane-sterilized soils were aerobically incubated with the bacterium normally alien to the soils for 48 and 168 h, respectively, with or without further additions of 10 ppm Cu to the soils with the bacterial cells. A pulverized quartz sand was included in the experiments to provide comparison. Unlike the immediate and sustained lethality of Cu revealed in sand suspensions, neither the previously nor the newly added Cu had any negative influence on the survival or proliferation of the added E. coli cells. The results thus showed that the soil Cu had no direct bactericidal or bacteriostatic effect. These data were therefore in accord with earlier suggestions that the Cu mitigates decomposition and resultant subsidence by inactivating degradative and accumulated soil enzymes that contribute substantially to the dissipation of their substrate-rich milieux. Key words: Copper, bacteria, organic soils, subsidence

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