Residual Zn Availability Related to Growth and Nutrient Gradients in Corn1

Responses to Zn application by corn (Zea maysL.) in the southeastern states have been few although Zn deficiency has been observed. This experiment was conducted to evaluate residual Zn availability related to growth and nutrient gradient and to explore reasons for the lack of Zn response. Residual Zn levels were determined in corn tissue grown on Norfolk is (Typic Paleudult) in 1974 after Zn applications of 0 to 30.3 kg/ha in 1971. Zinc concentration in recently matured leaves sampled in 1974 at the five leaf stage was 20 μg/g for the control and 46 μg/g for the 30.3 kg/ha rate indicating that tissue Zn concentration of leaves sampled in 1974 continued to reflect Zn applied in the spring of 1971. Plant dry weight at the five‐leaf stage did not reflect Zn additions. A later sampling of the recently matured leaf at the eight‐leaf stage and ear‐leaf sampled at early silking continued to indicate residual Zn availability from added Zn. Plant dry weight at early silking and grain yield at harvest were not affected by Zn rates indicating that sufficient Zn was available in control plots for maximum plant and grain production. At all residual Zn rates, Zn concentration was greatest in leaf 1 (top) and declined to leaf 7 and remained constant to leaf 10 (bottom). The ear‐leaf (leaf 8) was not as sensitive to residual Zn rates as the young leaves near the top. The Mn concentration gradient in leaves from top to bottom was 40, 54, and 36 for leaves 1, 4, and 10, respectively. Copper concentration was constant from leaf 1 to 10 and was not affected by Zn rates. Iron concentration increased gradually from 68 to 98 μg/g in leaf 1 and 10, respectively, and remained constant over residual Zn rates.