| Abstrakt: |
The Long‐Term Sludge Experiment (LTSE) began in 1994 at nine UK field sites as part of continuing research into the effects of sludge‐borne heavy metals on soil fertility. The long‐term effects of Zn, Cu, and Cd on the most probable numbers of cells (MPN) of Rhizobium leguminosarumbiovar trifoliiwere monitored for 8 yr in sludge‐amended soils. To assess the statutory limits set by the UK Sludge (Use in Agriculture) Regulations, the experimental data were reviewed using statistical methods of meta‐analysis. Previous LTSE studies have focused predominantly on statistical significance rather than effect size, whereas meta‐analysis focuses on the magnitude and direction of an effect, i.e., the practical significance rather than its statistical significance. Results showed Zn to be the most toxic element causing an overall significant decrease in RhizobiumMPN of −26.6% during the LTSE. The effect of Cu showed no significant effect on RhizobiumMPN at concentrations below the UK limits, although a −5% decrease in RhizobiumMPN was observed in soils where total Cu ranged from 100 to <135 mg kg−1. Overall, there was nothing to indicate that Cd had a significant effect on RhizobiumMPN below the current UK statutory limit. In summary, the UK statutory limit for Zn appears to be insufficient for protecting Rhizobiumfrom Zn toxicity effects. Meta‐analysis provides effect size of Cd, Cu, and Zn in sludge on RhizobiumMPN in soils.Zn in sludge significantly decreased RhizobiumMPN in soil by −26.6%.Below UK limits, Cu in sludge decreased RhizobiumMPN in soil less than 5%.Cd in sludge had no significant effect on RhizobiumMPN in soils. |
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