Agronomy Talk

Agronomy Update

Why is My Corn Tipping Back and Potassium Deficiency in Soybeans

Published on Thursday, August 28, 2014

Projections are for another bumper corn crop in Ohio and Indiana. Time will tell if we beat the average yield for both states of 177 Bu./A. from 2013. As I travel around both states, however, it is not difficult to find ears of corn and spots in the field where corn is tipping back. With such ideal conditions during pollination, many growers are wondering why this is happening. To understand this we may need to review a little about pollination. 

With the cool temperatures this past year and the wide range in planting dates, there was plenty of pollen to go around, so it was not a lack of pollen. In fact, most kernels actually pollinated and then tipped back. The main reason the corn tipped back was that the butt end kernels pollinated much sooner than the tip end kernels.

Therefore, the plant aborted the tip end kernels to concentrate on the earlier pollinated kernels. In general, there is only about a four day window (it can range from three to five days depending on temperature) for an individual ear to pollinate the kernels that it will keep. Any kernels that pollinate after this time will generally abort. That four day window is extremely important!

There are quite a few conditions that will cause corn silks to come out slower. Here are just a few that I have seen in 2014:

  • Nitrogen - This year especially, I am seeing a lot of nitrogen deficiency (as the picture above shows). Nitrogen deficiency causes silks to come out slower, therefore increasing the amount of tipping back. Lower nitrogen rates also delays pollination so corn may come out of the field with higher moisture.

  • Populations - The higher the plant populations, the slower the silks will come out. This is just due to more competition.

  • Genetics - Hybrids with more potential kernels require more moisture to push out the silks, therefore you will see more tipping back on hybrids with more potential ovules.

  • Drought stress - Lack of moisture will cause silks to push out slower, resulting in tipping back.

There are numerous other things that can cause tipping back such as compaction, low fertility, levels and soil type. The main causes I have seen this year are nitrogen, plant populations, and genetics.

Potassium Deficiency in Soybeans

There have been some recent reports of potassium deficiency in soybeans. The exact reason why this is happening is unknown, although there are some common characteristics. In general, we are seeing more potassium deficiency in lower ground, in fields that don’t have as much tile (poorly drained), and in some of the headlands where there is more compaction.

Potassium is a cation. It needs to exchange with other nutrients from the root to uptake the potassium. If you have a root that is diseased or not in the best shape (due to compaction, too much moisture, poorly drained ground, etc.) then it may be more difficult for the plant to uptake nutrients such as potassium. Many times the plants that have diseased roots often are the ones showing few nodules as well as potassium deficiency.

Soybeans require a lot of potassium. It takes about 1.5 lbs. of potassium per bushel, so a 60 Bu. crop needs about 90 lbs. (which equates to 150 lbs. of 0-0-60). If your fields are showing potassium deficiency, be sure to take a soil sample just to be sure you are not running low.

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Author: Mark Apelt

Categories: E Indiana, Ohio

Tags: Agronomy, Agronomy Update

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