Editorial comment by Jerry Carlson
An article posted on the AgWeb site reported sightings of yellowing soybean leaves in some Midwest fields. Some of the reasons given: Potassium deficiency and iron chlorosis.
However, the Iowa State University fertility specialist cited in the article essentially said there’s nothing you can do to help satisfy that deficiency this season. Next year, he said, do a better job with fertilizing.
This is the link to the AgWeb article on yellow soybean leaves and potassium deficiency. It’s headlined, “The Curious Case of Yellow Soybeans.”
Fortunately I never took agronomy classes at Iowa State beyond the 200 level, so there wasn’t much permanent damage done. At least we didn’t learn, as one Iowa extension agronomist told a client of ours, “Leaves can’t absorb nitrogen. Only roots can take up nitrogen.”
My education in crop nutrition was much less academic, learning from the field experience of teachers like Carey Reams, Dan Skow, Dave Larson, Steve Westin, Jerry Scheppele, Bruce Tanio, Roch Gaussoin, Bob Streit, Don Huber, Michael McNeill, Arden Andersen, Bob Kremer — and many others. All these teachers and consultants knew that precision foliar feeding with the right nutrients and correct timing is a highly efficient way to help correct deficiencies in growing crops.
The tough part is knowing what’s deficient before yellowing or other symptoms emerge visibly. That’s why we urge you to learn the protocols of newly available sap testing services. Or at the very least, use the tissue testing services of excellent labs like International Ag Labs of Fairmont, MN, or Midwest Labs in Omaha.
Ramping up soil fertility is not an assurance of adequate micronutrient nutrition in the crop, either. A new guide published by No-Till farmer ($12.95) called “Everything you Need to Know About Micronutrients” explains on page 19 that soil fertility tests and leaf tissue tests have “poor” or “very poor” correlations with each other. Complex interrelations between the micros means that crops may be unable to take up some key elements because another is deficient.
As evidence of just one of many foliar feeding experiences we’ve had, here’s a photo of a soybean patch on some rented ground we farmed in 2013. Severe potassium deficiency was evident in late July and early August. We foliar-applied potassium sulfate which was blended for us by AgriEnergy Resources. It was, of course, “amplified” by WakeUP Summer as a surfactant/carrier/mobilizer.
We sprayed every other six rows with foliar nutrients. Here’s a photo of that field on August 25, 2013.
The bright green 6-row strips are those foliar-fed. We added 8 bu. per acre to the foliar-fed soybeans. If you have a $200,000 sprayer sitting in the shed after your second Roundup spraying, and someone tells you there’s nothing you can do about yellow soybeans, please explore the facts about foliar feeding.
You can read the entire story of our little project by downloading the PDF summary at this link. It is four quick-reading pages.