|
“Basically, if a person has
potassium deficiency, they are going to lose yields."
Lloyd Murdock
UK Extension Plant and Soil Scientist |
By Laura Skillman
PRINCETON, Ky., (July 15, 2005) – Potassium deficiencies in corn and soybeans
are common this year, creating the potential for stunted plants and reduced
yields.
“I’ve been here 34 years, and this is the worst I’ve ever seen,” said Lloyd
Murdock, Extension plant and soil scientist.
Likewise, the UK Plant Disease Diagnostic Lab at Princeton has not seen samples
of potassium deficiencies in corn prior to this year, although they do see it
yearly in soybeans, which require more potassium, said Paul Bachi, plant
diagnostician.
The primary cause of the deficiency is low levels of potassium in the soil,
which can be determined by soil testing. While UK recommends that soil testing
samples be limited to 20-acre plots, some single samples are collected from much
larger areas. This allows areas with deficient levels to be masked by those with
sufficient levels.
Other factors adding to the deficiency include anything that restricts or slows
root development such as compaction or dry soils, both of which are factors this
year. Plants take in potassium with water from the soil. The problem can be more
pronounced in no-till and minimal tilled fields because much of the potassium is
in the top few inches of soil and does not move down into the soil structure.
“Even with these other things, if a farmer had a good soil test, the crop would
be alright,” Murdock said. “I haven’t seen a field yet that had a proper soil
test, that’s had a potassium deficiency. What I have seen is fields that when
you test the overall field it looks good, but there are parts of the field that
may be parts of an old field where potassium was depleted and they’ve never
built it back.”
This year has revealed some practices that farmers need to reconsider. No. 1,
Murdock said, is that some people are not soil testing as often as they should.
In addition, they are using too large an area for a single sample for testing,
and compaction is not being checked but is building up in some fields.
Farmers should pay more attention to zone or grid soil testing, he said.
“You need to do it by zones, especially this year when you see where the
problems occurred,” Murdock said.
Potassium is important for top growth and root growth, and without sufficient
levels plants can become stunted with minimal root growth. Potassium deficiency
started with corn and has moved into soybeans. The deficiency in corn shows in
the bottom leaves as a yellowing around the edge that will become necrotic and
can kill the leaf and move to the upper leaves of the plant. In corn, it can be
mistaken for chemical damage.
“Basically, if a person has potassium deficiency, they are going to lose
yields,” he said.
Yield loss varies depending on the deficiency. Small plants can face a
tremendous yield loss because they will not recover. Most of the severe
deficiencies will reduce the yields by a third to one-half, but if the corn has
grown well with only some mild deficiency symptoms showing at the bottom of the
plant, losses are more likely to be about 5 percent, Murdock said.
Farmers generally should soil test every two to three years. Any areas of fields
showing potassium deficiencies should be sampled and tested this fall so
corrective measures can be taken.
Writer: Laura Skillman
270-365-7541 ext. 278
Contact: Lloyd Murdock,
270-365-7541 ext. 207Return to Main News page. |
