Potassium for Crop Production

Originally written for CCA Soy Envoy Blog 

Having spent my time as a CCA Soy Envoy writing about micronutrients, sulfur, nitrogen and phosphorus, it seems appropriate to close out the year focusing on potassium. Of the plant nutrients, potassium is part of the big 3—nitrogen, phosphorous and potassium (NPK). When I run soil tests in my area potassium is the most likely to be low, although some soils I work with can be high and stay high. 

Potassium helps plants withstand drought damage. It is also credited with general plant health and preventing lodging. Potassium helps the plant produce starch and transform sugars. This nutrient is also essential for photosynthesis. Potassium deficiency is characterized by yellowing and then tissue death starting at the edges of leaves in both corn and soybeans. This Iowa State University Bulletin has more information on potassium deficiencies. They go into some explanation of causes of potassium deficiencies other than low soil test.

In past years we have seen some drought-induced deficiencies in fields. Fields with good potassium levels to begin with seem to resist that deficiency better. We also thought we saw some compaction-induced deficiencies because of working and planting in wet soil conditions this spring. Several years ago, University of Illinois (UIUC) researchers hypothesized that we do not need potassium fertilizer. Research from other credible sources including the International Plant Nutrition Institute has called the researchers’ premise into question and disproved some of their findings. Emerson Nafziger, Ph.D., also argues for potassium fertilizer in this article.

Potassium is common in our Illinois soils because it is present in the crystal lattice of a prevalent clay mineral, illite. The nutrient seems to move in and out of the lattice depending on moisture. This makes potassium soil testing imperfect, but it is all we have to establish a scientific basis for determining fertility needs.

One reason that we test soils more often than the university recommendation is that it helps us keep better track of potassium. It has been my experience that crops do respond to potassium when soil test levels are below 230 pounds per acres. Ideal levels are considered to be 300 to 400 pounds per acre in Illinois. Potassium is critical to help weather a drought. Levels need to be high because availability goes down when soil is dry.

We do have clients with soils that have not needed potassium fertilizer in twenty years or more. These growers haven’t 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. 

One of my clients raised 80 bu/A wheat a few years ago after increasing his potassium fertilizer on that field. We do find that potassium levels sometimes remain low for several years as we attempt to build the nutrient up. We will then have a sudden and unexpected rise in soil test potassium. I will sometimes suggest 100 pounds per acre of potassium fertilizer to prevent wild swings in soil test levels even though soil tests would seem to indicate we can skip a year.   

Iowa State University has endorsed a moist soil test where they do not let the soil dry down. I have no problem with using the moist test, but we continue to use the Mehlich 3 extraction. I am not ready to give up on potassium testing even knowing the limitations of the test. We are going to continue to test frequently and recommend potassium fertilizer on soils that have low soil test levels, making adjustments as needed.

Fertilizer and Water Quality

Recently the City of Des Moines, IA decided to sue upstream counties because of the high nitrogen content in their source water.  You may recall my recent post about the Illinois Nutrient Loss Reduction Strategy, so this news illustrates why we need to do our best to implement the strategy.  The Des Moines Lawsuit details are in this Prairie Farmer article. 

Nutrient Removal App

A nutrient removal app was recently introduced.  The app is free, and free sums up what it is worth.  What good is it to know how much was removed from your soil if you do not know what was there to start with?  Removal charts are based on averages.  They are not based on the reality of what happens in your field and in your soil.  So load up the app if you want to play with it, but don't forget the soil test is still the most important part of your fertility program.  When you can get an accurate soil testing app, then you might have something.

To-Till Farmer

No-Till Farmer, like many publications delivers a daily or almost daily update.  Many of their articles are well done.  I have been saving those e-mails to share here sometime.  This article on Boron is very well done. 

This article on soybean yields contains some very good information.  Long term research like this is especially useful because it comes closer to imitating field conditions on the farm than short term plot research does.  This research indicates that soybeans following corn is good for soybean yields not matter what tillage practices are used.

Hypoxia

Today I attended a Soil and Water Management Seminar put on by Extension Service.  Overall it was a well doe program focusing on using biomass for fuels.  However there were other topics of interest as well. 

Dennis McKenna of the Illinois Department of Agriculture put together some interesting information about hypoxia.  the hypoxia zone varies from year to year, but it is always there.  The zone consists of areas in the Gulf of Mexico with less than 2 ppm of oxygen.  The low oxygen is caused by algae blooms that are fueled by nitrogen and phosphorous in deposited in the Gulf out of the Mississippi watershed.  The Hypoxia Advisory Committee says we need to reduce Nitrogen and Phosphorous in the Gulf by 45%. 

USGS says Illinois is the number one culprit.  It would appear that tile drainage is a big contributor to the problem at least of Nitrogen in runoff.  One interesting note was that even in areas where no fertilizer N was applied, nitrogen loss was still higher than desirable just because of high organic matter in Illinois soils.  Dr. Fabian Fernandez also has data that shows that Illinois Soil Phosphorus levels are higher than the agronomically justifiable level of 35 ppm on over half the soils in Illinois.  When P levels get that high, even small amounts dissolving in runoff can be a problem.

Where is this headed?  Maybe regulation, especially of P.  It looks like some incentives may be used as well.  Alternatives that could help reduce the Nitrogen problem are:  reduced usage, no fall application, cover crops, constructed wetland filter, and bioreactors.  Alternatives to reduce dissolved P are:  do not apply if levels are above 35 ppm, use sediment basins, use filter strips, till to reduce surface levels of P.  It is clear that in order to achieve national goals in improve surface water quality, there is a good deal of work to do.  It would appear that producers need to be even more careful than they have been in the past in order for goals to be accomplished without affecting production levels.

Nutrient Management Regulation

Nutrient management regulation is here with the finalization of rules in Florida.  Unfortunately I can't find anything on how the proposed water quality standards will be implemented.  It is difficult to tell what kind of hardship might be created.  FLORIDA WATER QUALITY STANDARDS
Another article in Agrinews talks about a group targeting Ag pollution in Illinois.  Ag related pollution I used to believe we could hold off regulations by good stewardship practices, but it looks like regulation is in our future.  A TMDL study is currently underway on the Illinois River.  This study could result in Florida-like standards in Illinois too.