CADMIUM-ZINC INTERACTIONS IN PLANTS AND EXTRACTABLE CADMIUM AND ZINC FRACTIONS IN SOIL

Abstract

Some municipal and industrial wastes have been applied to land to recover their plant nutrients. Some of these wastes contain Cd and other heavy metal contaminants. Many studies have been conducted on Cd-Zn interactions in plants and on forms of these elements in soils. We conducted the present study to relate Cd-Zn concentrations in plants to levels of Cd and Zn in soil recovered by several extractants soon after application of Cd and Zn sources to soil. Cadmium nitrate and ZnSO4 or Zn(C2H3O2)2 were mixed with a Zn-deficient Crowley silt loam soil (Typic Albaqualf), cropped with corn (Zea maya L.), and then cropped with Swiss chard (Beta vulgaria). Applied Cd significantly increased the Cd/Zn ratio in both crops, especially in Swiss chard, which accumulates heavy metals. A previously published sequential-extraction procedure was used to fractionate Cd and Zn in soil after the corn harvest. Results of statistical analyses showed the highest correlation between Cd uptake by each crop and the “carbonate” (0.05 M Na2EDTA-extractable) and “sulfide” (4 M HNO3-extractable) fractions of Cd in soil. Including other Cd fractions resulted in only slightly higher R2 values. Zinc uptake by each crop was best related to the “organic” (0.5 M NaOH-extractable) fraction of Zn in soil, and including the other Zn fractions did not affect the relationship. These results show that Cd and Zn uptake by corn or Swiss chard was not related to similar chemical fractions of these elements in soil, and that the Cd/Zn ratio in plant tops was significantly affected by both Cd and Zn applications to soil.