RESPONSE OF CORN TO ZINC FERTILIZATION

Zinc deficiency symptoms are frequently observed at the 4 to 6 leaf stage of corn (Zea mays L.) grown on limed soils of the Northeast. A 7-yr field experiment was conducted near Ithaca, NY to determine the corn yield response to fertilizer Zn. The soil was a moderately eroded, Mardin silt loam (coarse-loamy, mixed mesic Typic Fragiochrepts), moderately low in organic matter, moderately high in P and K, very low in Zn, and limed to pH near 7. Severe Zn deficiency symptoms had been observed on corn in previous years. Response to Zn also was studied in the greenhouse at three root-zone temperatures. Corn responded to fertilizer Zn in 6 out of the 7 yrs of the study. The response from one initial broadcast application of 8 lb/Zn acre was equal to 8 to 10 lb Zn/acre applied annually. Response to 4 lb Zn/acre applied in the fertilizer band at planting was statistically significant only after several annual applications were mixed with the soil by annual spring plowing and disking. Extractable soil Zn with diethylenetriamine pentaacetic acid (DTPA) (Lindsay and Norvell, 1978) and sodium acetate (NaOAc) (Greweling and Peech, 1965) were highly correlated, but the DTPA solution extracted three times more Zn. Less than 10% of applied Zn was accounted for by subsequent soil extraction with DTPA. In the greenhouse study, corn Zn content increased with temperature and with soil Zn additions. Response to band-placed Zn was greater at a lower temperature where root growth was reduced. Zinc deficiency in young corn plants can be expected when the DTPA-extractable Zn is 0.6 ppm or less, or the Zn concentration of the young corn tissue is 16 ppm or less. The Zn deficiency symptoms and the associated yield reduction can be prevented for at least 5 yr with a single broadcast incorporation of 8 lb Zn/acre.