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July 2011 Archive for Ask an Agronomist

RSS By: Farm Journal Agronomists, Farm Journal

Have your agronomic questions answered by a Farm Journal agronomist. E-mail us directly at, and we’ll respond on this blog to provide an interactive dialogue.

How Much Attention Should I Pay To Micronutrients?

Jul 25, 2011

Question:  How much attention should I pay to the type and amount of micronutrients in my soils?

Answer:  In our efforts to boost corn yields, the presence and availability of micronutrients will become an increasingly common factor that farmers will want to address. It’s rare that fields are suddenly deficient in a micronutrient. Usually there’s an underlying issue that is contributing to the problem, such as high soil pH, for instance. The other thing to consider is that nutrient deficiencies aren’t always easy to distinguish between at a glance. For instance, a sulfur deficiency often looks like a nitrogen deficienc. The only way to know for sure what nutrients your fields lack is for you to do soil and tissue tests. 
Be on the lookout for sulfur deficiencies in your crops.
You can easily misdiagnose this problem.

What Is the Correct Phosphorus-Zinc Ratio?

Jul 21, 2011

Question: What is the correct phosphorus - zinc ratio?

Answer:  We commonly use a ratio of 20 to 1 in central Illinois. Rules of thumb are risky to rely on, though.  I’d encourage you to have some tissue analysis done to determine what ratio your particular soils and crops need.

When weather turns dry, do corn roots stop trying to find moisture?

Jul 18, 2011

Question: With the wet spring and the summer turning dry, at what growth stage do (corn) roots stop going deeper to find moisture? 

Answer: If there’s no obstruction to the corn roots – no compaction and no horizontal layer – corn roots will grow and move down until they reach the water table. The roots will continue to grow as long as they have access to water and oxygen. If the water table drops, the roots will follow the water. Typically, during rapid growth stage, a corn plant will put on 1” to 1.5” of root growth a day, while your water table drops in only a few centimeters per day. If there is compaction or a horizontal layer, the roots will typically grow horizontally once they hit that layer until they can find a crack in the soil that allows them to grow vertically again. The common problem at that point is if the water table has dropped very far, the roots will not be able to keep up with it even though they’re growing vertically again. If temperatures get too high, roots begin to die due to the heat and lack of water. In a drought situation the roots typically die from the top down and not the bottom up. If you have compaction or density layers in your fields, you have to get them out of there. That’s one reason why we talk quite a bit about vertical tillage. Anther option, if you don’t have irrigation and your fields drain off water quickly, is to entertain the idea of installing gated tile to slow down how quickly your water table drops. That will take some planning and help from someone who specializes in this type of work, but it could be a good investment for future corn crops.

How Can I Estimate Corn Yield Potential?

Jul 12, 2011

Question: I have seen some information you had that shows how to estimate corn yield potential. Can you provide that again? 

Answer: Here’s the basic formula, and I’m also including a chart that shows how to estimate corn yield potential under various row spacings.
If you’re in 30-inch rows, use a tape measure to mark off 17 feet 5 inches in a row of corn.
Count the number of corn plants in the measured-off space. Subtract any corn plants that appear unlikely to produce a good, harvestable ear.
Once you determine the number of harvestable ears in the measured-off space, randomly select three to five ears to count rows around and kernels long and use the following formula to arrive at anticipated yields:
average ears x average rows around x average kernels long = Yield
I’ve inserted some actual ear, row and kernel numbers in the formula here to give you an example:
32 x 16 x 35 = 199 bu/acre
I would encourage you to implement this practice in four or five different locations within each field, and then average the numbers, to arrive at a fairly accurate result.
Keep in mind the formula does not take into consideration kernel depths. Based on weather conditions during kernel fill you may increase or decrease your yield by 5 to 10 percent.
As you evaluate plant stand numbers and ear counts, consider that you can benefit from getting those two numbers to more closely align with each other.
For example, if you have 30,000 plants/A and your ear count is only 27,000 ears/A, you have the potential to increase yields 15 to 21 bu/A by increasing your ear count to 30,000 ears per acre.
While the number difference between plant stands and ear counts cannot be eliminated, it can be minimized. In a corn-soybean rotation, the difference between the two would ideally be no more than 1,200. In corn-on-corn, with heavy residue conditions, the ideal difference between the two would be 2,000 or less.

Table 1. Length of row to equal 1/1000th of
an acre for various row widths
Row spacing
Row Length
13 feet 1 inch
13 feet 6 inches
17 feet 5 inches
23 feet 9 inches
34 feet 10 inches

*Information provided courtesy of University of Minnesota Extension Service.

Which Is Better: Flat or Round Seed Corn?

Jul 07, 2011

Question: I read your column about seed corn testing but didn’t see anything on using round seed versus flat seed. Do you have thoughts on one being better than the other?

Answer: We used to get that question quite a bit but not recently as today’s modern equipment can handle either rounds or flats. Our experience is that high-yielding genetics are high-yielding, regardless of whether the seed is flat or round. I would emphasize that you’re dealing with a living product, so how you handle that seed prior to planting and at planting is very important. Every kernel of seed corn is wrapped in a thin protective coat, called the pericarp, which covers the seed like skin and provides its first line of defense against insects and disease. The pericarp also helps shield the seed from any rough handling farmers may dish out during the planting and harvesting processes. Round seed can be a bit more vulnerable to damage because its germ area is not as well protected within the kernel as it is in flat seed. If you question whether the seed you purchased is in good shape, have it tested by an independent laboratory to determine the emergence level you can expect. Also, know as much as you can about where your seed is coming from. Ask questions and learn about the company’s quality standards and their quality assurance procedures. It doesn’t matter where the seed is sourced from as long as the seed quality is there.
Until soil conditions are right, don’t throw your expensive corn seed into the mud.
An exacting regimen goes into seed production.

What Can I Do To Improve My Seed Corn Germination?

Jul 05, 2011

Question: I had some problems with my seed corn germinating this year that I’m not sure how to prevent in the future. Any advice you could offer would be much appreciated.

Answer:  There are a variety of reasons you may have had problems—mechanical issues, how the seed was handled prior to or at planting or even the seed quality—any of those factors can have an impact on germination.  It’s always the farmer’s responsibility to know as much about the seed they purchase as possible, which can help minimize the potential germination problems. If you’re concerned about seed quality, you might consider investing in some seed testing of some of your seed lots next year to determine the expected germination of the products you purchase. There are three different tests that growers often invest in: cold germination, saturated cold germination and the pericarp damage test. Check with your local Extension office to determine where you might have such tests conducted in your area. If you wonder how to prioritize the seed you want to evaluate for germination quality, some potential candidates would include:
  • Discounted seed
  • Seed from suppliers you question
  • Seed you plan to plant first, probably in your coldest soils
  • Seed that will be planted in tough soils where the fields have a history of emergence and disease issues.
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