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The solid phases that control Cd2+ solubility in soils are poorly understood. This study was made to measure Cd2+ activity in nine slightly acidic to alkaline soils using competitive chelation, which avoids errors that may be caused by unknown Cd‐organic complexes that may be present. The Cd2+ activities measured in these soils varied widely, ranging from 10−6.61 to 10−9.31 M, and were inversely related to soil pH with a correlation coefficient (r2) of 0.95. The activities of Cd2+ in the soils could be predicted from the equation (Cd2+) = 106.5(H+)2. A solubility diagram was constructed for various Cd minerals using the thermodynamic data selected from the literature. The equilibrium constant (Ko) for the reaction of CdFe2O4(c) was derived assuming that the entropy (So) value of CdFe2O4(c) is similar to that of ZnFe2O4(c). The diagram suggests that CdFe2O4(c), in equilibrium with soil Fe, is a likely solid phase controlling Cd2+ activities in these soils.

Total content of Fe, Mn, Zn, Cu, Pb, Cd, Ni and Co in soils irrigated with sewage effluent increased with increasing years of using sewage effluent in irrigation. Iron and Co applied to the soil from sewage effluent were immobilized mainly in unavailable form; Pb, Cd, and Ni in moderately available form; and Mn, Zn, and Cu in highly available form. The concentrations of Fe, Mn, Zn and Cu in tops of alfalfa and leaves of corn grown on these soils increased substantially with increased levels of available metal content of the soil, while those of other metals were little affected. As for orange, continuous increase in leaves metal content with time was found for Fe, Mn, Zn, Co and Cd. The concentrations of Cd, Co, Ni and Pb in corn grains and orange fruits were several times higher than normal, and this reduces their suitability for human consumption.

Summary -ZusammenfassungSolutionsof Zn, Cu and Mn chelates of EDTA, DTPA and EDDHA were reacted separately with a calcareous soil for periods up to 28 days. DTPA was an effective chelate for Zn and Cu; more than 77 and 55 70 of the added Zn and Cu, respectively, remained soluble after 28 days of reaction with the soil. The stability of Zn-EDTA and Cu-EDTA was relatively less than those of the respective DTPA chelates, whereas Zn-EDDHA and Cu-EDDHA were highly unstable in the soil. The loss of soluble Mn from Mn-EDTA, Mn-DTPA and Mn-EDDHA additions to soil was very rapid and completed in about one week.It was found that adsorption of Zn-EDDHA, Cu-EDDHA and Mn-EDDHA molecules by the soil was the main process removing Zn, Cu and Mn from solution. Whereas, replacement of the metal in the metal-chelate molecule by Ca ion from the soil was a more serious factor affecting the stability of DTPA and EDTA chelates of Zn, Cu, and Mn. Reaktion von EDTA-, DTPA-und EDDHA-Komplexen von Zink, Kupfer und Mangan mit einem kalkhaltigen BodenLosungen von Zn-, Cu-und Mn-Chelaten von EDTA, DTPA und EDDHA wurden getrennt mit einem kalkhaltigen Boden in Reaktion gebracht. Die Reaktionsdauer betrug bis zu 28 Tagen. DTPA war ein wirksames Chelat fur Zn und Cu. Mehr als 77 bzw. 55% des zugefiihrten Zn und Cu verblieben nach 28 Tagen Reaktionsdauer in der Losung. Die Stabilitat der Zn-EDTA-und Cu-EDTA-Chelate war vergleichsweise geringer, wahrend die Zn-EDDHA-und Cu-EDDHA-Chelate im Boden sehr instabil waren. Die Loslichkeit der drei Mn-Chelate nahm schnell ab und war nach einer Woche verschwunden.Es wurde gefunden, daS die Adsorption von Zn-EDDHA, Cu-EDDHA und Mn-EDDHA der Hauptprozess des Zn-, Cu-und Mn-Entzuges aus der Losung war. Dagegen war der Ersatz der Metall-Ionen durch Ca-Ionen im Chelat bei den DTPA-und EDTA-Chelaten der wichtigste Faktor, der die Stabilitat beeinfluate.

Natrium ‐ (Calcium + Magnesium) ‐ Austauschgleichgewichte in Böden. Beckett's approach has been used to describe the Na‐(Ca + Mg) exchange isotherm in twenty soil samples that differed in texture and salinity. The data obtained from the isotherms were compared with the values of exchangeable sodium obtained by ammonium acetate and the concentration ratios (Na/ °Ca+Mg) calculated from the saturation paste extract. The Na‐Q/I relation was always linear for each of the studied soils with no curvature at the lower values of concentration ratio. Values of ‐ Δ Na0 obtained from the isotherms were highly correlated with exchangeable Na (r2 + 0.89). The equilibrium concentration ratios of the isotherms were similar to those obtained from the saturated paste extract in the non‐saline soils, and were much lower in the case of the salt affected soils. The slope of the Na‐Q/I relation appeared to be a soil characteristic not affected by either Na depletion from the soil or Na addition up to 5 me./100 g. soil. The PBCNa values were highly correlated with the C.E.C. values of the soil (r2 + 0.97).

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