Department of Soil Fertility and Management, Agricultural University of Norway, 1432 Ås-NLH, Norway
An account is given of two pot experiments, of which one has included all combinations of 5 heavy metals (cadmium, cobalt, lead, mercury and nickel), 3 rates of each metal, 2 rates of lime, and 3 types of soil (clay soil, peat soil and sandy soil). The experiment has run for 4 years (1973 —1976). Two parallels have been used for each treatment. A third parallel without crop has been used for soil sampling only. The second experiment has run for 3 years (1974 —1976), and has included the same soil types and lime rates, but only cadmium and mercury of the metals. The crop grown in all years has been oats. 250 mg/pot of all metals except lead have had a distinct yield reducing effect. In the case of mercury, the reducing effect ceases from the third year. It decreases gradually after nickel throughout the experimental period, but not after cadmium and cobalt. Heavy liming (pH 6—7) has almost eliminated the yield reduction after nickel, and has considerably reduced it after cobalt. The contents of cadmium, nickel, cobalt, and mercury in the yield have been multiplied with the application of 250 mg/pot of the metals mentioned. Application of even 0.5 mg/pot of cadmium resulted in a distinct increase of content both in grain and straw. 0.5 and 5 mg mercury, however, had only slight effect. The content of the metals decreased throughout the experimental period. The effect of mercury in the fourth year has been minimal, even after the highest application rate. Lead application led to only moderate increase in the content of the yield. Roughly 45—55 percent of the added rates of cadmium, nickel and cobalt, as a mean value for the soil series, has been recovered as AL-soluble at light liming with pH approximately 5. Heavy liming has reduced the uptake by 3—7 percent for cadmium, by 16—20 percent for nickel, and by 22—24 percent for cobalt. Generally, the amounts of AL-soluble metal in soils have decreased in the order: series peat > sand > clay.
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