You like the concept of $4 corn and you are planning to do everything possible to produce as much as possible. You have increased corn acreage in your rotation. You have booked more nitrogen (but haven’t told anyone.) And you are planning to boost your plant population. But the question is, how much? What is the perfect stand of corn?

That was the rhetorical question asked by Extension Crop Production Specialist Emerson Nafziger of the University of Illinois recently at one of many crop conferences. (Proceedings Page 45) “Many producers have increased their targeted plant population in corn in recent years yet still wonder, after a year with good weather and good yields, whether they should have set the planter for higher populations than they did.” Does that describe you?

Nafziger says yields at some research plots:
1. show yield increases beyond 40,000,
2. some begin to fade at 35,000, and
3. some begin to fade at 30,000.
Those statistics are a relationship between soils; and despite the expense of the seed, he says there seems to be little risk in pushing populations above 30,000 per acre in the more productive soils.

What about the variability of spacing between corn plants? After all you are not digging holes, separated by the length of your foot, and putting two kernels and a fish in each one. Nafziger says some serious debate has occurred among crop production specialists about the variability of plant spacing and its impact on population. After all, planters are not infallible; but he says, “Faster planting speeds increased plant spacing variability slightly but had no effect on yield.” But he says where there are a lot of plants missing, and spacing between kernels varies by 4-5 inches or more, population and yield will drop. Conversely, if plants are thinned to an even stand, there is little effect on yield. In the end, Nafziger says, most agronomists now believe that, while perfectly spaced plants down the row is the ideal, there is likely to be little yield loss under the small amount of variability,” which he defines as 3 inches or less deviation in the spacing from one seed to the next. “As a general rule, spending money to try to improve a stand that is less than perfect but within an acceptable range probably will not increase profits much, if any.”

What about the variability of emergence and plant maturity? Nafziger says uniformity and plant size early on will diminish yields more than non-uniform plant spacing. The key to uniform emergence is a uniform planting depth. He says the optimum depth is 1.5 to 1.75 inches, and more or less will probably mean a lack of uniformity of soil conditions and create a variety of emergence. As planting depth drops from that level, so does yield potential. Plants that are not as large as those around them will have a greater challenge in competing for light and moisture, and will be unable to produce an equal amount of grain as those around them.

What about the grade of the seed affecting yield? Quick and uniform emergence has an impact on plant uniformity and ultimately on yield. Nafziger’s research finds little yield variation based on seed grade. Whether you are planting flats or rounds, whether you are planting large or small seed, the yield fell within a couple percentage points of each other. Different planters may differ in distribution of seed, but Nafziger says once it is in the ground, seed grade will have little affect on yield.

Summary:
The key to an optimum stand of corn generally is uniformity, both in depth and in spacing. But those will not guarantee a good yield if there is not good contact between the seed and the soil and if there is an insufficient amount of moisture. The uniformity will guarantee that each plant has an equal chance at light and moisture. But the grade of the seed makes little difference in the yield, unless the planter has trouble with uniform distribution of that particular grade.