BY FLOYD KOEHN
To those of you who might follow National Corn Growing yield contests, you will have noticed that a new record corn yield was set again last year. David Hula of Charles City, Virginia, grew a yield of 623.84 bushels an acre. It is quite intriguing how this is done. Obviously, we won’t grow that kind of corn in Central KS, but we can learn something from those that do.
The climate or the environment that corn grows in is a huge factor. In fact, it is probably one of the biggest yield enhancers or detractors. Our climate is not conducive to growing this kind of corn.
Let’s start with a few facts gleaned from some university research. The average kernel size in the U.S. is .25-.3 grams a kernel. The average bushels of corn raised per thousand plants is 6-7 bushels. So, if you plant 30,000 plants and have a final stand of 28,000 and you have a decent year, you could expect 168-196 bushels per acre yield.
These averages are taken across a wide geographical area, so we know that they don’t necessarily apply to us in all situations. The truth is that we have yielded a lot higher than this and a lot lower than this.
Dryland yields are the wildcard in our area. In a drought year, we can have corn that yields near to nothing, and in good years, corn can be produced in the upper NO100′ s and, in some extreme cases, go as high as 200. Some farmers have an average production history (APH) of around 100 bushels an acre. These are obviously made up of extremes.
Let’s review the things that make a difference that we can influence, along with rain or lack of rain. Fertility, compaction, population, uniformity of stand, kernel count on the ear, kernel retention, and kernel density.
It goes without saying that we need good fertility. We need nitrogen applied before or at planting to have it available when the plant needs it. Corn uses nitrogen the most efficiently if applied several times through the growing season. We need phosphorous, potassium, sulfur, manganese, zinc, and boron, to name some of the nutrients. A good quality starter fertilizer goes a long way to a good beginning. The first thing that a corn plant needs to do is build the factory that makes the grain. A robust root system is where it all starts. We want the roots to go down and out at an angle. If the roots hit a compaction layer, they will go sideways. This limits their ability to find and utilize water and nutrients in the soil. If corn is planted in soil that is too wet, you get sidewall compaction, and roots will be compromised and follow the seed slice. Proper soil conditions at planting are essential for a corn plant to have a good beginning.
Compaction was already mentioned, but this one is huge. It is not uncommon to have a tillage-induced compaction layer that will hinder water infiltration and root development. You can measure compaction with a penetrometer, and when compaction goes over 200 psi, it hinders root development, and over 300 psi, it literally stops root penetration. This test needs to be done in moist soil. If roots can’t penetrate the soil, neither can water easily move through the soil. Corn roots, if unhindered, can go as deep as 4 feet.
When you drive through our community, you will see a field of corn that looks nice and green, and right across the road, it will be brown and burning up. Compaction is likely a contributing factor.
Dryland corn can be planted as low as 18,000 seeds per acre, and some irrigated fields will approach 35,000 seeds per acre. Water is the determining factor in deciding how much corn is planted. Corn uses a lot of water, and if you don’t have or anticipate getting enough water, you just plant less.
The winners of the National Corn Grower’s yield contest plant 50,000 seeds per acre. They have everything that it takes to feed and nourish that plant. We don’t have that here.
18,000 corn plants an acre will produce a respectable yield in a good year and will not fall apart right away in a bad year. The reader might ask, what makes the difference? It is about kernel size, count, and density. More on that later.
Uniformity of stand is critical to get maximum yield from the population that is planted. The record yield corn growers watch emergence like a hawk. They want every plant to come up within twenty-four hours of the same time. It is essential that this happens because the corn plants need equal competition with each other. When a plant gets delayed at emergence, it receives less space to grow roots and less sunlight and stays behind all season. The result is that you get a small ear or an ear that is not harvestable.
When I go into a field and count stands at roasting ear stage or soon after, I will only count the ears that are of a uniform size. You can drop 30,000 seeds per acre at planting, and you may only have 25,000 uniform ears.
When a farmer takes his planter to the field, he has several crucial items that he wants to watch. A good seed bed is comprised of uniform moisture, not too wet or too dry, even planting depth, even soil temperature, and even seed spacing. He also wants the soil temperature to be a minimum of 50 degrees Fahrenheit with a warming trend in sight. This is ideal but not always optimally possible. It has been said that a farmer has done 70% for a crop by the time he pulls his planter out of the field.
It is extremely educational to walk corn fields at harvest and pull back all the husks on 1/1000th of an acre. That is 17.5 feet of row length on thirty-inch rows. Do this several times. Better yet pick all those ears and take them home and lay them out and compare them with each other. I will hand shell the ears after I have picked them, weigh the corn from each ear, and weigh the kernels to see how heavy the kernels are. At a minimum, weigh several of the ears and see what you find.
A typical ear will have 14 to 18 rows of kernels and will be anywhere from 30 to 40 kernels long. This will give you anywhere from 420 to 720 kernels on an ear of corn. Some simple math here will help us understand how much difference this will make. As was stated earlier, the average yield per thousand in the U.S. is 6-7 bushels per thousand plants per acre. Good corn can make and often will yield 10 bushels per thousand plants per acre. This amounts to 9 ounces of dry corn per ear.
So, if you can raise 9 ounces of dry corn per ear, you can take your population times 10 and get your yield. 20,000=200, 30,000=300, and on up. The champion yield winners plant 50,000 or maybe a bit more per acre, and that’s where 500-bushel corn comes from. Last year, the winner got what he called bonus ears, which is a second ear on the plant. Most corn will only produce one ear per plant, but when the conditions are right, it will push a second ear. We seldom see that in Central KS at 30k population, but we do see it at lower population levels or when we have a skip, and the plant has more room. It gets more sunlight and more nutrients and responds accordingly.
Here is where kernel density and depth start to make a difference. Corn is sold as a 56-pound bushel. It is not uncommon for high-yielding corn to weigh as high as 62-64 pounds a bushel. The record grower this year had corn that weighed 66 pounds a bushel. Let’s suggest that an ear has a mid-range of 576 kernels that weigh .3 grams a kernel. 576 kernels times .3 is 172.8 grams of corn. This is 6.09 ounces of corn per ear. If we have 28,000 ears, we have a total of 10,657 ounces of corn, which equates to 190 bushels an acre.
A kernel weight of .4 grams gives us 8.12 ounces of corn per ear, which amounts to 253.75 bushels per acre. If we can push the kernel count a bit and get a bit heavier kernel, we suddenly have 300-bushel corn within our reach.
The following was copied from the Iowa State website. “Common kernel weights range from 0.25-0.30 grams per kernel. For yield estimation, a correction factor of 65,000 to 110,000 kernels per 56-pound bushel is used; 90,000 is most commonly used. If your crop is subject to stress before R6, starch accumulation in the kernels is reduced, so you will have a lower kernel weight. In this case, you will want to adjust the kernels per bushel upward. If your crop grows in nearly perfect conditions, the value can be adjusted downward.”
As I have counted and weighed corn, I have seen as few as 60,000 kernels a bushel of really dense high test weight corn, and as many as 143,000 kernels a bushel of drought-stressed corn. Last year, I heard of new math relative to corn, and that is that three equals two. If you have really deep kernels, you can lay three of them end to end, and they will measure two inches long.
Corn either dies down or dries down. Too much of the time the reason a corn plant becomes mature is because it died an unnatural death. We see this especially in dryland corn. Often, it is too hot and dry when the plant is in its’ final stages of maturity because of a lack of water, and it just dies. If you drive by a field of corn and the ears are hanging down, the ear is no longer being nourished by the plant, and it is what it is. If we can keep the plant green and the ear upright until the corn is around 20 percent moisture, it will have packed the maximum amount of starch and nutrients into that kernel, and it will have a heavy test weight.
Kernel retention is also a factor. A plant will pollinate more kernels than it can raise at times. If it doesn’t have enough fertility or moisture, it will start to tip back or abort kernels on the tip of the ear. We can try and mitigate this by keeping the corn watered and providing late-season nutrition.
It takes 9 ounces of dry corn per ear at a 30k population to make 300-bushel corn. Can we do that in Central KS? I don’t know, but I think it will happen someday. If we push the population higher and get most of the ears to fill to their inherent ability, we might even get there. On our farm, I would like to get all the variables that we can influence right, raise 300-bushel corn, and then go beyond that. Wishful thinking, perhaps, but something to work for.
In summary, I want to talk about stressors. Someone once said that a corn plant never wants to have a bad day. The stressors that we experience in South Central Kansas are shallow soil, too much water, too little water, too much heat, and nights that are too warm. Central Kansas summer nights tend to be quite warm. The temps can be in the upper 70s and low 80s during grain fill. This is not good for corn.
We experience high wind events that cause green snap and occasional hailstorms. We could add insects and fungal diseases to that, but they would be secondary. If we do everything else right, these are not always issues. I believe that we can have an impact on the first three and the last two with regenerative farming.
The rest we will have to leave to nature, but remember that a healthy plant always has a better chance of success.
I enjoyed visiting with you about corn.