from the October 4, 2009 Newsletter, issued from the Siskiyou Mountains west of Grants Pass, Oregon:
NUTRIENT DEFICIENCIES IN CORN

Above you see a corn leaf blade in the garden. It's easy to be wrong when diagnosing illnesses but I'm thinking that the leaf's problems are caused by deficiencies in both potassium and phosphorus. Here are the main corn-blade symptoms of deficiencies of the main nutrients:

NITROGEN: general yellowing of plant, especially toward tips of blades

PHOSPHORUS: purple coloration on blades

POTASSIUM: Yellow and brown coloration of blade margins

SULFUR: on younger blades, yellow striping running lengthwise between veins

ZINC: on upper blades, yellow striping starting at midrib in center of blade, then may progress outward

The blade in the picture displays the purple of phosphorus deficiency, plus its yellow and brown margins suggest potassium deficiency. Both of these deficiencies may result from our garden's heavy, clayey soil, and the corn having been planted when the ground was still cold this spring. Corn planted later when it was warmer now stands taller and shows fewer nutrient deficiency problems, and even has fewer aphids.