By Brian Hefty

If you asked me which nutrient I would guess to be the most likely to be low to deficient in my fields, my answer would probably be potassium.  We have seen major potassium issues all across the country.  Here are some tell-tale signs you’ve got a problem, along with what you can do about it.

  1. LODGING/SMALL STALKS.  I don’t care what crop you plant.  If your crop has lodging issues, it could certainly be related to compaction or drainage, but it has little to do with the variety you plant.  The most likely cause is lack of potassium.  In other words, if your corn (or any other crop) falls over in a wind this summer, DO NOT CALL THE SEED DEALER!  Certainly, the variety makes a slight difference in standability, but all your other agronomic factors play a much bigger role, with potassium levels leading the way as the top lodging factor.
  2. YELLOW LEAF MARGINS.  Most people blame late-season lower leaf yellowing on dry weather (e.g., “My corn is firing!”).  However, when you look closely at the leaves, you will often see a yellowing on either the leaf margins (potassium deficiency) or up the midrib (nitrogen deficiency).  By the time you see yellowing, you have already lost a good percentage of your yield.
  3. POOR GRAIN QUALITY.  The are many factors that affect this, but potassium plays a major role in things like test weight, dry-down, and other grain quality issues.
  4. LOW SOIL TESTS.  I don’t care what your parts per million number says or if someone calls that low, medium or high.  What I want to see on your soil test is that your base saturation percentage is 4 percent or higher.  Until you get that number at 4 percent or above, expect to see at least some problems with lodging, yellow leaves, and poor grain quality.
  5. DEFICIENT TISSUE ANALYSIS.  Sampling plant tissue is a great way to make yourself a lot smarter.  If you’ve never done this before, start like this:  With GPS coordinates or flags, mark two spots in a field; mark the best area and the worst area.  Then, sample for ten consecutive weeks.  On our farm, we sample at 8 a.m. every Monday morning so we have consistency.  With grass crops like corn and wheat, start testing as soon as they emerge in the spring.  With broadleaf crops like soybeans, we generally start our ten weeks of testing about a month after emergence if we plant on time.  After you get the results from ten consecutive weeks, you will have a really good idea if potassium is an issue on your farm.

What do you do if you are short on K?  Most importantly, you should get more in your soil in the fall, spring and/or at planting-time.  We often apply a lot in the fall and more in-furrow when we plant.  We have also done some side-dress work, but by the time you realize you have a deficiency and want to apply more K, you have already lost yield.

Keep in mind, too, that applying K in the short-term doesn’t always make economic sense.  Quite often, the K you apply now will help your crop for several years, so it is important to look at the long-term returns besides just this year.  We strongly encourage you to do a good job with soil testing and using plant tissue analysis.  If you do, you will be able to better invest your fertilizer dollars.