Influence of Redox Potential and Plant Species on the Uptake of Nickel and Cadmium from Soils

Abstract

The influence of soil redox potential on the uptake of nickel and cadmium from three soils was studied in a pot experiment with oat (Avena sativa L. cv. Pirol) and rye-grass (Lolium multiflorum L. cv. Lema). The soils used were a Luvisol (naturally low in Ni and Cd), a sewage-sludge amended Luvisol (anthropogenic enrichment of Ni and Cd) and a Cambisol (naturally high in Ni and Cd). Nickel and Cd supplied in sewage-sludge amendments were several times more available for plant uptake than those present naturally in the soil. Short term decreases in soil redox potential, as a result of soil flooding, had little effect on the availability of Ni and Cd from sludge amended soils, but resulted in a substantial increase in Ni and Cd availability in the soil naturally high in Ni and Cd. In general, increases in soil solution concentrations of Ni and Cd, due to sludge amendment or changes in soil redox potential, resulted in increased Ni and Cd concentrations in the aerial parts of plants. Nickel concentrations in the grain of oat increased with increasing Ni concentration in the soil solution, whereas grain Cd concentrations did not. In contrast, Cd concentrations in vegetative parts of both oat and rye-grass were strongly affected by soil type and sludge-amendment. In all treatments Ni concentrations in the grain were much higher than in the vegetative parts, whereas Cd concentrations were always higher in vegetative parts than in the grain. Tissue Ni concentrations correlated well with DTPA extractable soil Ni but only poorly with total soil Ni. Differences in the availability and uptake of Ni and Cd in response to soil type, environmental conditions and plant species suggest that the use of total soil-metal content to regulate the use of sewage sludge on agricultural land is inappropriate.