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Fig. 4. Relationship between observed and fitted values of Cd concentrations in wheat grain. Fitted values were calculated from the regression models including (a) total soil Cd and pH as variables as in Eq. [1] for the paired soil and crop surveys; (b) total soil Cd, pH, and cultivar terms for the paired soil and crop surveys; (c) total soil Cd and pH as variables as in Eq. [2] for the two long-term sewage sludge experiments; and (d) total soil Cd and pH as variables as in Eq. [3] for the combined data set.
