Distribution and plant availability of soil copper fractions to oat (Avena sativa) nutrition in Haryana soils

The distribution of copper (Cu) among various chemical forms and its availability to oat nutrition may vary significantly in response to changing soil properties. Therefore, a pot and laboratory study were conducted to investigate the distribution of native and added Cu fractions and their plant availability to oat (Avena sativa L.) nutrition in eighteen (18) different soils of Haryana that varied in physical and chemical properties. Seven-step sequential fractionation showed that most of the total Cu (51.12%) was associated in the residual fraction (RES). The percentage of soil Cu in the exchangeable fraction (EX-), carbonate bound (CARB-), organically associated (OM-), Mn oxide bound (MnOX-), amorphous Fe oxide bound (AFeOX-) and crystalline Fe oxide bound (CFeOX-) fractions averaged 2.71, 0.74, 2.74, 0.21, 13.35, and 29.11%, respectively. Amount of Cu in MnOX, AFeOX, CFeOX, RES-fractions and total Cu were interdependent and varied directly with DTPA-extractable Cu and clay content. On the basis of stepwise regression analysis, the residual fraction contribute very little whereas exchangeable and carbonate bound fraction contribute maximum to the availability of Cu to oat plant. The concentration of Cu and its uptake in oat were positively correlated with DTPA-extractable Cu, MnOX-Cu, AFeOX-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 Haryana soils.