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The objective of this study was to find a suitable extractant(s) for plant‐available metals in metal contaminated soils. Swiss chard (Beta vulgaris L. ‘Fordhook Giant’) was grown in greenhouse pots on 46 Ontario soils varying in degree of contamination with metals. The soils had been contaminated with metals to varying degrees over a period of years. After 40 days, the plants were harvested and Zn, Cd, Ni, and Cu concentrations were measured. Each soil was extracted with nine different extractants: aqua regia, 0.01M EDTA, 0.005M DTPA, 0.02M NTA, 0.5N CH3COOH, 1N CH3COONH4, 0.6N HCl + 0.05N AlCl3, (COOH)2 + (COONH4)2, and H2O. Zinc, cadmium, nickel, and copper concentrations in Swiss chard were correlated with the amounts of soil Zn, Cd, Ni, and Cu removed by each extractant. Of the nine soil extractants, CH3COONH4 was the best predictor of plant‐available Zn if only extractable Zn and soil pH were included as independent variables in a regression equation. Acetic acid was the best extractant for prediction of both plant‐available Cd and Ni when soil pH was included in the equation. Attempts to find a suitable soil extractant for plant‐available Cu were unsuccessful.

Long-term fertilizer-P application affects soil-P distribution and forms. These effects must be characterized to use fertilizer P most efficiently. In three southern Ontario soils of varying texture, we determined changes in soil organic P (Po) and inorganic P (Pi) caused by fertilizer P application (0–90 kg broadcast P ha−1 yr−1 during 10 yr of corn production. Soil P was characterized by (1) annual measurement of 0.5 M NaHCO3-extractable P (Olsen-P) and (2) sequential extraction from soil taken at the beginning of the experiment and after receiving 0 to 90 kg broadcast P ha−1 yr−1 for 10 yr. Fertilizer P increased Olsen-P concentrations in all soils. The increases were proportional to the cumulative amount of P applied. Based on all three soils, 16 kg P ha−1 was required to increase Olsen-P concentrations by 1 mg L−1 soil. After 10 yr of 90 kg broadcast P ha−1 yr−1, labile Pi fractions (resin P and NaHCO3 P) were increased, as was NaOH-extractable Pi in all soils. On the most P-deficient soil (Conestogo SiL), where corn grain yields were increased by fertilizer P, P fertilization also increased HCl-Pi, residual P (H2O2-H2SO4 extractable P) and labile Po (NaHCO3-Po and NaOH-Po). A P balance was calculated, which accounted for additions to, removals from, and changes in the total P status of the 0–20 cm layer. When no broadcast P was applied, there was an unaccounted-for input (possibly from the subsoil), of 20.9 kg P ha−1 yr−1 on the Conestogo SiL. When 90 kg broadcast P ha−1 yr−1 was applied to the Fox SL, the coarsest soil studied, there was a deficit of 30.9 kg P ha−1 yr−1 and elevated Olsen-P concentrations in the 25–36 cm depth, suggesting downward movement on fertilizer P. It appears that subsoil P was involved in the P cycle of these two soils. Key words: Continuous corn, P fertilization, sequential extraction, organic phosphorus, inorganic phosphorus, labile phosphorus, subsoil P, leaching

This study was conducted to determine the chemical distribution and plant availability of Cd, Zn and Ni in eight metal-polluted soils in southern Ontario, Canada. There were altogether 30 different soil samples because two of the soils had received various sewage sludge treatments. The soils were sequentially extracted with 1 M ammonium acetate to remove soluble plus exchangeable metals, with 0.125 M Cu(ii) acetate to remove complexed metals, and with I M HNO3 to dissolve chemisorbed or occluded metals and precipitates such as oxides and carbonates. Expressed as a percentage of the metal so extracted, exchangeable Cd>Zn and Ni; complexed Cd and Zn>Ni< and Ni>Zn>Cd in the acid-soluble pool. With a few exceptions (soils with high organic matter content or low pH) at least 50 per cent of the extracted metal was in the acid-soluble pool. The percentage of metal complexed was significantly correlated with organic matter content. The percentage of metal in the acid-soluble fraction was significantly correlated with soil pH. Preliminary findings based on the results with two soils suggested that for Cd and Zn plant availability was correlated with the concentrations of exchangeable, complexed or acid-soluble pools ofCd and Zn.

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