Uptake of native and applied copper by corn and wheat as related to soil properties

Copper and Zn deficiencies of crops have been reported in various parts of the world. To prevent these deficiencies sulfate forms of Cu and Zn are generally used. In addition, Cu and Zn also are contributed to soils by manures, pesticides, and waste materials such as sewage sludge. An insufficient supply of Cu or Zn may reduce crop yield; whereas, excess Cu or Zn may be detrimental to both plant and animals.

The field phase of this research was conducted on a Davidson silty clay to evaluate corn response to high levels of CuSO₄ and ZnSO₄ applications up to 338 kg Cu and 830 kg Zn ha⁻¹. The results of this research indicated that corn grain and stalk yields of corn were not affected (α= 0.05) by high levels of CuSO₄ and ZnSO₄ either alone or combined. Copper concentration in neither corn grain nor ear leaves was affected (α = 0.05) by the Cu application. Zinc concentrations in both grain (α = 0.01) and ear leaves (α= 0.001) were increased by ZnS04 application. Application of ZnSO₄ increased the Cu in the labile pool, whereas CuSO₄ fertilization did not affect Zn in the labile pool.

A greenhouse experiment was conducted to examine the response of wheat to Cu application on 14 soils. Treatments in this study were a control and 5.35 mg Cu kg⁻¹ as CuSO₄. Dry matter yields were not affected (α = 0. 05) by Cu fertilization whereas tissue cu levels were increased (α = 0.001). Copper uptake was highly correlated with DTPA-Cu (r = 0.80, α = 0.001), but weakly correlated with Mehlich III-Cu (r = 0.28, α = 0.05). The DTPA-Cu showed high correlations with clay content (r = 0.98, α = 0.001) and SA (r = 0.93, α = 0. 001); whereas, Mehlich III-Cu did not correlate with these variables (α = 0.05).

A second greenhouse experiment was conducted with 10 Virginia soils to evaluate the response of corn to Cu fertilization. Treatments were a control and 5.35 mg Cu kg⁻¹ as CuS0₄. Dry weights of corn on the 10 soils were not affected (α = 0.05) by Cu application; whereas, tissue Cu levels were increased by the applied Cu (α = 0. 001). Copper uptake by corn plant correlated with DTPA-Cu (r = 0.62, α= 0.001) and with soil pH (r = 0.35, α = 0.05). There was no correlation of organic matter with Cu uptake (α = 0.05). Both DTPA-Cu and Mehlich III-Cu were unrelated to either organic matter or soil pH (α = 0.05).