DISTRIBUTION AND PLANT AVAILABILITY OF SOIL COPPER FRACTIONS IN SASKATCHEWAN

Growth chamber and laboratory studies were conducted to investigate the distribution and plant availability of copper (Cu) fractions in Saskatchewan soils. These studies included an examination of the distribution of Cu fractions in 27 soils and an evaluation of plant availability of native and added Cu fractions in beans (Phaseolus vulgaris L.) grown in seven soils. The soils in these experiments were selected to give a wide variation in physical and chemical properties. Total Cu content of the 27 soils ranged from 6.5 to 39.0-mu-g g-1 with an average of 21.0-mu-g g-1. A seven-step sequential fractionation showed that most of the total Cu (49.0-78.0%) was present in the residual fraction (Res-). The percentages of soil Cu in the exchangeable (Ex-), Pb-displaceable (Pb-), acid soluble (Aci-), Mn oxide bound (MnO-), organically associated (OM-) and Fe, Al oxide bound (FeO-) fractions averaged 2.2, 1.5, 2.0, 4.8, 7.9 and 11.1%, respectively. Amounts of Cu in MnO-, FeO-, Res- fractions and total Cu were interdependent and varied directly with DTPA- extractable Cu and clay content. The growth chamber experiment showed that the most of the applied Cu was accumulated in MnO-, OM-, FeO-, and Res- fractions. Therefore, sesquioxides and organic matter are the major components responsible for the adsorption of added Cu. The concentration of Cu and its uptake into navy beans were positively correlated with DTPA-extractable Cu, MnO-Cu, FeO-Cu and total Cu, which in turn were correlated with clay content. Plant Cu concentration and uptake can be predicted by an equation which includes DTPA-extractable Cu and clay content. These results showed that DTPA-extractable Cu is a good predictor of Cu availability in prairie soils.