Field studies were conducted over a three-year period with corn at a total of 82 site-years to evaluate the zinc (Zn) status of Illinois soils. Sites were selected that had soil chemical or physical properties favoring Zn deficiency, including high pH or Bray Pl extractable P, low organic matter, sandy texture and/or suspected of showing Zn defi­ciency symptoms. Soil extractable Zn was determined with three extractants: DTPA, EDTA-)zC03 and 0.1N HCI. Zinc was applied as ZnEDTA at 1. or 2 lb Zn/ac before planting. Whole plant samples were taken at the six-leaf stage and ear-leaf samples at silking and analyzed for Zn content. Grain 

yields were also determined. Soils from each of the locations from the second two years of the field experiment were also evaluated under greenhouse condi­tions. Two corn crops were grown successively, each for a length of 40 days, and dry matter yields and Zn concentration determined.

In the field experiments, significant grain yield response to Zn applications occurred at only 3 of 82 locations with an average increase of 14 bu/ac. The average yield increase for all sites was 1.4 bu/ac. Soils at 19 sites tested below critical levels for all three extractants but did not respond to Zn fertilization. The application of Zn to soil under field conditions did not significantly increase Zn concentratios of either the six-leaf stage or ear-leaf samples at any sites.

Greenhouse studies indicated no increases in plant dry matter with applied Zn for either the first or second crop­ping but increases in Zn concentration in whole plant samples occurred for both crops.

It is apparent from this work that the calibration studies that have been performed for the extractants used are not applicable to the soil types and conditions existing in Illinois. The study suggests that Zn deficiency is of minor agronomic concern in the central Corn Belt and that unfavorable soil chemical characteristics alone, such as low extractable Zn and/or some other property that would indicate reduced availability, can not be relied upon to indicate a need for Zn fertilization.