2005 Year in Review

From the Fields – Potassium Deficiency

Source: Jim Morrison, Extension Educator, Crop Systems, Rockford Extension Center, University of Illinois, Phone 815/397-7714; FAX 815/397-8620; Email: morrison@uiuc.edu

Some field corn in northern Illinois is exhibiting potassium or potassium-like deficiency symptoms. The young corn seedling does not need much potassium, an essential plant nutrient, but the rate of uptake increases rapidly after the V6 stage to a peak in the three weeks prior to tasseling.

In corn, potassium deficiency first appears as a yellowing and browning of the leaf margins beginning at the tips of the lower leaves and extending down the margins toward the stalk. The outer leaf edges appear scorched or fired while the midrib remains green. This differs from nitrogen shortage because the discoloration is along the margins of older leaves rather than the midrib area. Potassium is mobile in the plant in that it moves from the old to the new leaves, thus the top leaves appear normal unless the potassium deficiency is extreme, and then the entire plant is yellowish. Another symptom is reduced plant growth or stunted plants with leaves close together (shorten internodes).

What causes the deficiency symptoms? Obviously, one reason is low soil test potassium level. In addition, there are other soil factors that affect the availability of potassium., and in turn affect root growth, root mass, and overall root and plant health.

Low soil moisture reduces or limits the uptake of the nutrient by corn roots, especially if there is a lack of vertical distribution of potassium in the soil. Compacted soil layers have increased bulk density resulting in a reduced plant root density and thus less potassium uptake. Seed furrow side-wall compaction and shallow planting depth are other contributing factors. Poorly aerated, wet, strongly weathered soils, poor soil tilth, and very acid soils also limit potassium availability. Sandy soils and heavy potassium removal by the proceeding crop also favor the deficiency. Lastly, seedling diseases can greatly reduce effective rooting, thus inducing potassium deficiency symptoms.

Stalks of potassium deficient plants are weak and may lodge later due to increased susceptibility to stalk rot. Ears on potassium deficient plants may be small with pointed, poorly developed tips.

Many times the symptoms appear first on ridge-till systems, then no-till and followed by reduced tillage systems.

Since potassium is relatively immobile in the soil, any factor restricting or reducing root growth can decrease uptake of the nutrient. In many situations, potassium is present in the soil, but simply not available to the plant for one or more of the reasons mentioned above. So what can be done to correct the problem? Very little, if any corrective actions can be taken now. Soil testing in affected and not-affected areas can help determine future potassium needs or whether a change in potassium application may be warranted. Management strategies to promote good rooting and use of planting techniques to insure rapid seedling growth should be helpful.

by  Editor, theCity1.com
July 6, 2005