Sep 23, 2014
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March 2014 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 do I maximize populations for maximum corn yields?

Mar 24, 2014

Question: It seems to me that the high population talk is a trap by the seed companies.  If they would breed a good flex-eared hybrid so we could plant at 25,000 to 28,000 population, we would be much better off in a year like 2012. Also I am not aiming for 250 bushels when my maximum yield potential is only 200 to 220 bushels. A 45,000 to 60,000 population may be fine for test plots but not for whole farms. How can we afford seed at the high populations?

Answer: You’re right in your thinking.  But you have to intermingle ear type with leaf structure.  So, if we’re trying to conserve water any year in any soil type, we want to reduce populations because they consume less water.  But as soon as you reduce populations, as you’ve noted, you need a good flex ear.  You need a hybrid that will flex and get you back to where you want to be in yield.  You also need to look at leaf structure.  In genetics, there’s what we call three leaf types: upright, pendulum and semi-upright.  You also need to capture at least 96% of the sunlight out there to maximize yield.  So, if you lower the population fewer plants means you need bigger leaves and in a pendulum format. Those leaves need to flop out in the row to capture that sunlight. Then, you need an ear style, a flex ear, that can make up that difference.  When we talk about a 45,000 to 60,000 population we’re talking about a very upright leaf structure that allows the sunlight down inside the canopy so plants capture that sunlight to produce food. And we’re also talking about a very determinate hybrid. So you need to push populations to make yield, because the ears won’t flex as much; they have an upright architecture to let sunlight deep inside the canopy.  If you lower populations with an upright hybrid you could burn up and lose all your water if too much sunlight gets in. If you lower populations with a determinate ear you can give up too much yield because the ear won’t flex to make up that difference.  So, in this format, you’re correct. What if you chose a flexed ear in 25,000 or 28,000 and did it on less population? You’ll need a pendulum leaf structure versus an upright structure so you can capture the sunlight to produce the yield you’re looking for.  You’re going to need to get between 7 bu. and 10 bu. per 1,000 population and not the 5 bu. or 6 bu. that we usually look for. So we’re talking about high populations, determinate ears and upright leaf architecture. We’re also talking about low populations to manage water and flex ears and a very pendulum leaf architecture.  You have to marry both of these two up.  It’s amazing how much yield today we have given up by pushing populations too high for the leaf structure we’ve got.  The problem with flex-eared hybrids is if you push them too hard, they flex both ways. They can flex yields off.  Determinate hybirds, if you don’t push them they won’t yield.  But if you push them they’re more resilient and won’t back up. If you’re going to lower the population you need full flex and you need pendulum leaves—you’re looking for both of these characteristics in the hybrid.

Seed to Success

The first step in variable-rate populations is working with a seed representative to select the right hybrid.


Zero In On Population

Improvements in seed corn genetics have resulted in hybrids that perform best when planted in higher populations.


Calculate Your Soybean Seeding-Rate Needs

Soybean seed costs have risen, farmers don’t want to plant more seeds than they need for top yields.


Do you recommend inline ripping in the spring?

Mar 12, 2014

Question: I have been an agronomist in central Iowa for 20 years and have been in the mind set of heavy tillage to manage compaction and residue and turn the soils black for spring.  I still have to manage residue and compaction but I want to switch to a vertical tillage system to increase soil health.  I will be practicing what I preach for the first time as I enter into my own farming operation.  I was not able to get in to the farm early enough in the season before the ground froze, to inline rip the bean stubble.  What has your experience been with a spring ripping with an inline? Thanks for your comments!

Answer:  When we’re talking about inline ripping we’re talking about going between 12" and 14" deep to get full width shatter for vertical tillage. Typically, that is half the distance of your spacing. So, if the spacing on your shanks is 30" apart, then you need to go 15" to get full width shatter so your vertical tillage program will work.  I would not recommend 15" ripping in any spring, because you need freezing and thawing in multiple cycles to get the soil to settle after you rip it 15" deep.   If you rip it in early early spring, after that window of opportunity, you never know how much freezing and thawing of the soil you’re going to get and it won’t settle. That can leave you at a high risk of the soil drying out. The soil can dry out very rapidly, so you get the crop caught in a drought situation early.  Or, the other thing that happens is you don’t get freezing and thawing but you get heavy spring rains. Because you fractured those soils your water infiltration rate is probably going to be 3x or 4x. If you fill the soil with large amounts of water, you may not be able to get fields planted in time.  The risk of drying out or too much water is too high a risk. If I’m determined to do spring tillage, I might switch to a chisel plow and chisel the field 7" deep on 14-inch centers.  I would chisel plow in the spring then level that field with my vertical tillage harrow in a matter of hours. As we do tillage in the spring, we kick out clods, what I call watermelon rinds, and when they blow apart you need to be there.  You have to do very timely vertical tillage. Some guys will chisel all night long and then go back and level fields that morning. In the day, I may only be able to chisel a couple of hours before I need to go back and level up the soil. The reason is if those clods of dirt dry out, you’re not going to be able to break them apart. A good practice for a check on this would be to hold a clod of dirt shoulder high drop it to see if it blows apart.  While it sill breaks up is when you want to get in there and level up the field. Do not chisel all your ground and then come back in two weeks and try to level up that field, because you’re not going to get rid of the clods.  Or, you’re going to have clods you can’t get rid of because there’s no more freezing and thawing. The ideal time to do your primary vertical tillage pass would have been shortly after harvest.


What could cause crooked growing corn?

Mar 07, 2014

Question: What could be the problem when corn grows crooked in several fields different locations?   This corn was irrigated with circles and rill irrigation. 

Answer: It’s hard to define what you are talking about by crooked, but I’ll assume it means the corn’s got a crook in it at the crown so like it was growing one direction and then turned and straightened itself out.  There are two things I have seen that cause crooking at the crown. One is severe rootworm pruning, where the plant lodges or wants to lodge, and this is early in the season. The corn tips over one way or the other and then it stands itself back up.  If it’s a rootworm problem it’ll go multiple directions so that the corn is crooked. You can identify this by looking at the crown roots and brace roots for rootworm damage. The other issue that can cause crooked corn is when soil becomes saturated, you get a high wind, and the corn is pushed over so that it leans over one direction and then it fixes itself and straightens back up and has a crooked look to it.  If all the plants have the same crook in it and is leaning the same way, it’s probably a function of high winds and the result of overly saturated soils or too loose of soil. You can’t do anything about a high-wind situation, but if it’s rootworm pruning you need to change your insecticide program and consider changing up your traits.  Attend to this very quickly if it’s a rootworm problem.  If it’s just a fact that high winds caused the corn to lodge there’s not much you can do. You can’t fix this really unless you go to no till or reduced tillage, if it’s a wind issue. 


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