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This is the year to see nutrient deficiency symptoms. The sodden spring followed by our current dry spell have created soil conditions that are not conducive to good root growth and development. The development of K deficiency in corn is a prime example. The peak period of K uptake occurs from 4 to 8 weeks after seed-ling emergence, and, during this period, as much as 5.0 lb./acre/day is taken up by the crop. If early root growth and the development of nodal roots has been restricted by too wet and/or too dry conditions, the plant will simply not have an extensive enough root system to meet the shoot’s nutrient demands.
Most K deficiency symptoms appear in the period between 15 inches and tasseling. Symptoms appear first on the lower leaves. Potassium is a “mobile” nutrient so it can be moved from older to younger leaves when the K needs of the younger leaves are not being met by K uptake by roots. The older leaves turn yellow and the leaf tissue along the margins (leaf edges) starts to dry-up and die back (necrosis).
If more severe K deficiency develops, the older leaves die back and yellowing symptoms and marginal necrosis appear on the younger leaves. Plant height may be reduced, silking delayed and mature ear size reduced. Stalk diameter may remain unchanged, but K deficient plants may lodge late in the season because stalk strength is lower and plants are more susceptible to stalk rots.
Plant analysis can be used to diagnose K problems during the growing season. Whole plant samples taken 30 to 45 days after emergence should contain 3 to 5% K. Ear leaf samples taken at early silking should contain between 1.7 and 2.5% K. The ear leaf taken at early silking is the best indicator of plant K status, but if the plant is found to be K deficient very little can be done during the current growing season to correct the problem. In general, K applications made later than 6 weeks after emer-gence are not economical because the peak period of plant K demand (4-8 weeks after emergence) may have been missed entirely.
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The Corn Growers Guidebook , a WWW resource
for corn management systems in Indiana and the eastern CornBelt.
Purdue University Agronomy Extension WWW
Home Page.
Purdue Agronomy On-Line! , Purdue's Agronomy
Department WWW Home Page.