Distribution and plant availability of soil copper fractions following copper sulphate and farmyard manure applications

The effects of copper (Cu) application on the Cu distribution in various po ols were investigated in laboratory and pot culture experiments with two Al fisols. The total soil Cu was fractionated into water-soluble plus exchange able (CA-Cu), inorganically-bound (AAC-Cu), organically-bound (PYR-Cu), oxi de-bound (OX-Cu) , and residual (RES-Cu) forms. The relative contribution o f these fractions to Cu uptake by wheat was calculated through path coeffic ient analysis, a statistical technique that differentiates between correlat ion and causation. Copper fertilizer was applied at rates of 0, 5, and 10 m g (kg soil)(-1) and FYM at rates of 0 and 10 t ha(-1). Results indicated th at the amounts of Cu present in CA-Cu were very small. The CA-Cu, AAC-Cu, P YR-Cu, and OX-Cu fractions were increased and RES-Cu was not significantly affected by the Cu application. No significant variation (P less than or eq ual to 0.01) was observed between Cu application with and without FYM on th e distribution of different fractions of soil Cu except PYR-Cu in Patancher u soil. Among the levels, application of 10 mg Cu (kg soil)(-1) showed the maximum increase in different fractions of soil Cu. The per cent increase i n Cu concentration in different fractions followed the order CA-Cu > AAC-Cu > PYR-Cu > OX-Cu > RES-Cu. The path analysis showed that the PYR-Cu and AA C-Cu are the most important fractions for maintaining the available Cu pool in soils.