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Form and Availability of Copper and Zinc in a Rhodic Paleudult Following Long-Term CuSO₄ and ZnSO₄ Applications¹

ABSTRACT

Copper and zinc frequently are incorporated into agricultural soils as fertilizers, pesticides, and waste materials. Field data are needed to determine rates of cumulative Cu and Zn applications that cause yield decreases or accumulations of the micronutrients in plant tissue. This 15-year field experiment was conducted on a Davidson silty clay (clayey, kaolinitic, thermic Rhodic Paleudult) to determine tolerable levels of Cu and Zn applications for corn (Zea mays L.) and to evaluate soil distribution and form of the applied Cu and Zn. Neither corn grain nor silage yields were affected by 15 years of applications of various levels of Cu and Zn sulfates, which provided a cumulative total of 171.7 kg Cu/ha and 290.4 kg Zn/ha. Copper concentrations in ear leaves sampled at the early silk growth stage generally were unaffected by the Cu applications, whereas Zn concentrations in the ear leaves varied directly with levels of Zn application. Likewise, the Cu concentrations in corn grain were unaffected by the Cu applications, but the Zn concentrations in corn grain were increased by the Zn applications. The DTPA-extractable Cu and Zn in soils sampled in the 13th year of the study indicated an accumulation of Cu and Zn in the Ap horizon, with little downward movement of the applied Cu and Zn. Sequential extraction data indicated that the applied Cu and Zn were distributed among both potentially plant-available and -unavailable soil fractions.

Key Words: Cu and Zn fractionation • Cu and Zn mobility • Cu and Zn uptake • DTPA-extractable Cu and Zn • waste disposal

¹ Contribution of the Dep. of Agronomy, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. Research was supported in part by the International Copper Research Association Inc.

² Graduate Research assistant, Professor, Graduate Research Assistant, and former Graduate Research Assistant (now Assistant Professor of Agronomy, University of Georgia, Athens, GA 30602), respectively.

Received for publication December 26, 1981.