Effect of Fertilizers and pH on Retention of Copper by Soils

Retention of copper applied in the form of CuSO₄ to three soils— black, red and sandy loam—was studied and it was observed that the black soil retained a higher amount of applied copper in comparison to the red and the sandy loam ones because of its high organic matter and total carbonate contents and higher pH value. However, in the presence of nitrogenous and potassic fertilizers the retention of Cu by the soils decreased appreciably. This decrease in retention is supposed to be due to antagonistic effect of NH₄ and K ions and also due to lowering of the equilibrium pH. The amount of “fixed Cu” (i.e. Cu which is not extracted by 0.1N H₂SO₄) has been found to increase whilst the exchangeable Cu (i.e. Cu extracted by N BaCl₂) decreases as the dose of N and K fertilizers is raised.