Illinois Research about Potassium Soil Test

University of Illinois Researchers have raised some concerns about Potassium Soil Testing.  The Prairie Farmer covered the story and the end has a link to the paper as written. 

I know that potassium soil testing is imperfect, but it is all we have for a scientific basis for determining fertility needs.  We do have clients that have soils that have not needed potassium fertilizer in twenty years or more.  We have not had any apparent yield loss and the test levels remain high.  We also have clients who have low potassium test levels who have benefited from potassium fertilizer.  I have one fairly new client who raised a field of wheat that yielded 80 bushels per acre for the first time ever this year.  His potassium levels were low, but his phosphorous levels were fine.  We upped his potassium fertilizer and improved his yields a good bit. 

Another indicator of the need for potassium fertilizer is symptoms of deficiency.  This Iowa State University Bulletin has a good discussion of potassium deficiencies.  They go into some explanation of causes of potassium deficiencies other than low soil test.  We have seen some drought induced deficiencies, but not in all fields.  Fields with good potassium levels seem to resist that deficiency better. 

I am not ready to give up on potassium testing even knowing the weaknesses of the test.