The effect of some heavy metals on oats in a pot experiment with three different soil types

Abstract

An account is given of a pot experiment comprising all combinations of 5 heavy metals (cadmium, cobalt, lead, mercury and nickel), 3 rates of each metal (0, 50 and 250 mg/pot), 2 rates of lime, and 3 types of soil (clay soil, peat soil, and sandy soil). Crop yields of grain and straw are given in Table 2. Low addition of the metal (50 mg/pot) has had slight or no effect on the yield size. The high rate of metal (250 mg/ pot) of some of the metals has induced definite to heavy yield reductions. Nickel has led to a heavy yield decrease in all soil series both in grain and straw afterlight liming. The yield reduction is to a certain extent or completely eliminated after heavier liming. Mercury has induced a near complete crop failure in the sandy soil series at both lime rates. Some yield reduction is obvious also in the other soil series, in clay soil only after light liming. Cadmium has reduced the straw yields in peat soil after both lime rates. Clay soil shows grain yield reduction at heaviest liming, while no yield reduction is detectable in the sandy soil. Cobalt has induced some degree of yield reduction in all soil types, most of all in clay soil after light liming. Lead has had no effect on the yield size. The heavy metal content in the crop is presented in Table 3. Apart from lead, the relative content increases very heavily with increased metal application. The content at times proves essentially higher in the crop from peat soil and sandy soil than in crop from clay soil. The content of cadmium, nickel and cobalt is lower at heavy liming compared to light liming. This is particularly characteristic of the crop from clay soil and sandy soil. The effect of heavier liming on the mercury and lead uptake is equivocal. For nickel, the relative content is essentially higher in the grain than in straw. The content of other metals is higher in the straw. The lead content in particular is much higher in straw than in the grain. In addition to the crop experiment, all treatments have included one parallel pot without plants. At the harvesting time, samples were taken from these pots for chemical analysis. The heavy metal content was determined after extraction by an AL-solution (Table 4). Wide variations appear between metals and soil types with regard to the recovered amounts of applied metal. Mercury shows a characteristically low AL-soluble recovery, only 1 to 2 per cent at the highest application rate. Also of lead, only a small amount of the applied substance exists as AL-soluble. With regard to the remaining metals, nearly all have been recovered as AL-soluble by a heavy application of cadmium to sandy soil at light liming. In other cases the percentage recovery falls within the 20—70 range, the lower figures often pertaining to clay soil and the higher ones to peat soil. A description of plants influenced by retarded growth, and symptoms of toxicity, are given.