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C.O.R.N Newsletter 2004-28
     August 23, 2004 - August 31, 2004


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Do Not Overlook Potassium
by Robert Mullen

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Considering the importance of nitrogen (N) and phosphorus (P) fertilization, potassium (K) is sometimes overlooked. Even though K does not get the same attention as N and P, it is an important nutrient for crop production. Potassium serves two major roles in higher plants, 1) enzyme activation and 2) osmotic potential maintenance (water dynamics). Plants that are K deficient are less able to regulate transpiration (water exchange between the plant and air) resulting in poor water use efficiency. Thus adequate levels of K are needed to support high-yielding crops.

Because K exists as a monovalent cation (K+) (a single, positively charged element), it is not extremely mobile in the soil, and its mobility increases as soil texture becomes coarser. Thus heavier textured soils have a greater capacity for adsorbing K. When identifying if soil K levels are adequate, cation exchange capacity (CEC) is considered. Based on Tri-State Recommendations, the following table shows the relationship between K critical values and CEC:

CEC (meq/100g) ___ Critical Value (lb/acre)
5 _________________ 175
10 ________________ 200
20 ________________ 250
30 ________________ 300
Potassium levels below the critical value are deficient and are likely to respond to application of K fertilizers. To see current state recommendations for K, refer to the Tri-State Fertilizer Recommendations available at your local Extension office or on-line at http://ohioline.osu.edu/e2567/.

Readers can subscribe electronically to this newsletter by signing up at http://agcrops.osu.edu/services/email.html. E-mail labarge.1@osu.edu if you have problems subscribing or no longer wish to receive this newsletter.

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.


Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868

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