Copper amendments and soil ph affect distribution of different chemical forms of metals and their uptake by Swingle citrumelo seedlings

Abstract

This study was conducted to evaluate the effects of various rates of Copper (Cu) amendments (as CuSO₄.5H₂O at either 0, 25, 50, 100, 200, or 400 mg Cu kg^‐1) to soils with different pH values on the distribution of various chemical forms of Zinc (Zn), Iron (Fe), Manganese (Mn), and Aluminum (Al) in soils and their uptake by Swingle citrumelo citrus rootstock seedlings. The soils included Myakka fine sand (pH 5.70), Candler fine sand (pH 6.45), and Oldsmar fine sand (pH 8.16). The chemical forms of metals evaluated in this study included exchangeable, sorbed, organically bound, precipitated, and residual forms. An increase in Cu rates, lowered the pH in the Myakka and Candler fine sands, but not in the Oldsmar fine sand. This, in turn, resulted in an increase in the proportion of the readily soluble forms (the exchangeable + sorbed forms) of Zn and Mn, and decreased that of Fe in the Myakka and Candler fine sands. In those two soils, the organically bound forms of Zn, Fe, and Mn decreased with an increase in Cu rates. However, the proportion of readily soluble forms was not significantly influenced by increasing Cu rates in the Oldsmar fine sand. The total content of Zn, Fe, and Mn in citrus roots and that of Zn and Fe in the leaves, significantly decreased with an increase in Cu rates in the Myakka and Candler fine sands. In the Oldsmar fine sand, Cu rates through the entire range had no significant effects on the total contents of Zn, Fe, and Mn in the leaves or in the roots of Swingle citrumelo rootstock seedlings.

Keywords:

• Antagonism
• chemical forms
• copper phytotoxicity
• metal uptake
• micronutrients
• sequential fractions