WATER SOIL RATIO INFLUENCES AQUEOUS-PHASE CHEMISTRY OF INDIGENOUS COPPER AND ZINC IN SOILS/

The effect of dilution on the composition of soil solutions of 8 contr asting soils ranging in pH from 5.3 to 8.8 with reference to zinc (Zn) and copper (Cu) was studied. Soil samples were equilibrated with wate r in various water:soil ratios for 24 h. Equilibrium solutions were ex tracted and analysed for dissolved organic carbon (DOC), and major and minor elements. The separation of the soil solution at field capacity (FC) was carried out by a drainage method. Although the concentration of ions decreased upon dilution, the total quantity of sodium (Na), p otassium (K), Zn, Cu, and DOC extracted per unit of soil weight increa sed. In contrast, the total quantity of Ca and Mg decreased in most so ils. The ratio of Zn and Cu to Ca correlated to dilution level, wherea s the ratio of Zn to monovalent cations decreased in low pH soils. The relationship between the quantity of Zn and Cu at different levels of the water:soil ratio in the soils studied showed that the concentrati on of these trace metals at FC soil moisture can be estimated from the soil extract. Increases in soil moisture content led to a marked chan ge in the ion-pair, free hydrated metal concentrations, and complexati on. Log Zn2+ was linearly related to solution pH. Zinc solubility was not consistent with published solubilities of any common minerals. Als o, Zn solubility in alkaline soils tended to be higher than reported v alues in the literature, indicating that soluble metal-organic ligand complexation was underestimated in these soils. The relationship betwe en pH and log Zn2+ was affected by dilution in several ways.