Was an ALS herbicide used recently that might be having some residual activity affecting the corn?
Answer: An ALS herbicide was used as a burndown, and may indeed have damaged the corn. Cool weather and high soil pH exaggerate ALS injury.
Additional Tests:
Measure soil EC and plant height to determine whether there is a correlation between the two.
Measure soil and plant tissue N to determine whether there is a correlation between N levels and chlorosis of lower leaves of plants in outer rows.
Measure soil and plant tissue P to determine whether there is a correlation between P levels and purpling of lower leaf margins of some plants in middle rows.