Effects of EDTA on the uptake of micronutrient metals by oats from an organic soil

Abstract

It has been shown, in a pot, culture trial, that the addition of EDTA to a neutral, manganese-deficient, organic soil increased the uptake of native manganese by oats. However, manganese uptake from large additions of manganous sulphate was lowered in the presence of EDTX. EDTA increased the uptake of iron and copper from this soil by oats at all yield levels. No increase in uptake of iron, copper, or manganese occurred if EDTA was added to the same soil limed to pH 8. These results are discussed in relation to other reports of the effect of EDTA on plant uptake of micronutrient metals from solution and from soils. It is pointed out that aluminium may replace divalent metals in EDTA complexes added to soils. Such substitution might occur more rapidly at pH 8 than at pH 6-7 because of the larger amount of aluminium in solution at the higher pH. It is suggested that this reaction may explain the failure of EDTA to increase uptake of micronutrient metals from the limed soil in these experiments. Uptake of copper and iron from the untimed s oil, in both presence and absence of added EDTA, appears to be linearly related to total transpiration of the oats during their growth. It is thought that this may reflect the dependence of oats in this soil on soluble anionic metal complexes brought to the roots with soil moisture. In a second pot experiment, uptake of added manganese was increased by EDTA added 3-4 weeks after the manganous sulphate. In this case the manganous sulphate would have been mostly oxidized when the EDTA was added. It is suggested that EDTA may speed up the biological oxidation of manganous salts in neutral soils. If this were so, plants not treated with EDTA in the first experiment might have absorbed more added manganese early in their growth and maintained a higher manganese content throughout the season than plants treated with EDTA. In the second experiment, the effect of EDTA on manganese oxidation would be largely eliminated, and the effect in increasing water-soluble manganese in the soil mould become discernible. In this second experiment, EDTA prevented the occurrence of grey speck disease, whereas addition of hydroquinoue failed to do so. Nevertheless ,plants treated with hydroquinone contained as much manganese as, or more than, those treated with EDTX. This result is discussed in relation to the "manganese requirement," of oats.