Oklahoma State University

General Information

General Information

Potassium is a relatively immobile nutrient. This being so the need is not related to yield to rather related to concentration in the soil. When a soil test is returned the analysis whether reported in ppm, Soil Test K, or lbs per ac is related to the sufficiency of P in the soil.

Potassium is mobile in the Plant so deficiencies will appear in lower leaves as yellowing around the out edges.

As a note Soil Test K as reported by OSU SWFAL is essentially lbs/ac. PPM *2 equals lbs/ac of a 6" soil sample.

 Special Considerations 

K under Drought Conditions

Potassium deficiencies can be induced by dry soil conditions.  Potassium is taken up by plant primarily through the process of diffusion into the roots.  This process is facilitated by water, in drought conditions the film of water that surrounds the roots becomes too thin and the plant has difficulty pulling K into the root. 

Much of the fields that show K deficiency symptoms in Oklahoma in dry periods are often fields that also have low to moderate Soil Test K levels.  This brings out two points, the dry weather increases the impact of the low soil K levels and that a application of K fertilizer may have prevented the issue.

An additional note is that Drought induced K deficiencies do not also exhibit the Classic K symptomology. In a few cases the deficiencies will develop in the middle of the plant, not on the oldest leaves as typically seen but also not on new growth. 

Correcting the Problem
Correction of drought induced K deficiency lies in prevention.  During the dry period very little can be done.  Once crop receives rain and soil moisture is replenished deficiencies will be corrected. Since K is mobile in the plant (why symptoms develop on old leaves) the yellowing will never go away. 
As mentioned Soil testing and proper pre-plant fertility will dimenish the likelihood of experiencing this problem.

 KCorn_Rose Mayes CoKSoybean_Keesee Hughes Co

Additional Resources

Wiebold & Scharf U of Missouri  K Deficiency symptoms in drought-stressed crops. 

Voss ICM Dry Weather Induces K Deficiency. 

Voss Iowa State Drought Induced K Deficiency followup.

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