Sins committed at planting aren't likely to be forgiven as the growing season progresses, especially in the case of corn production. “You can't recover from the sins of planting,” says Dewy Lee, University of Georgia Extension agronomist.
There are a multitude of such sins, says Lee, including planting too fast, planting too deep or too shallow, planter malfunctions, not managing conservation-tillage residue and not using irrigation properly to achieve a good stand.
“All of these are things that happen at the very beginning — things that you may very well be able to affect,” he says. “Obviously, there are things over which we have no control, including rainfall and seed germination. But germination of corn seed typically hasn't been a problem for Georgia growers.”
The results of problems that occur early in the year include stand variability, loss of depth control, traveling too fast and uneven emergence because of any one of these problems. “All of these problems — in some form or fashion — lead to yield loss. And, in most cases, they're quite preventable,” says Lee.
These problems, he continues, have an effect on plant spacing variability. “That is how uniformly seeds are distributed in the row, and it can affect yields and cost you money,” he says.
Plant spacing variability come in many forms, notes Lee. “You may find that you have crowded plants here and there, and you may have large gaps between plants. In other words, if you're planting for 6 inches, you may have some plants that are 3 inches apart and other that are 7 or 9 inches apart. Or, you may have a mixture of crowded plants and gaps.
“We see a lot of these with plate planters and less with vacuum planters. Yet, I still go into fields every year, where growers are using very expensive equipment, and I see plant spacing variability.”
One of the effects of a gap, says Lee, is a reduction in grain yields resulting from a plant population that often is less than optimum. An optimum plant population for irrigated corn is in the high 20,000 to low 30,000-range. In a dryland environment, optimum may range from 16,000 to 24,000 plants per acre, depending on soil type.
“What about if you get an occasional double? It actually may enhance your yields as long as the doubles don't exceed the threshold capability of that hybrid. In other words, if the threshold is 35,000 plants and we see a decline in yields after that, and we see a few doubles, they will hurt rather than help you.”
If variable spacing is a mixture, which is the case in most fields, the effects usually will be negative, says Lee.
A study of 354 fields, mainly in Indiana and Ohio, looked at the yield losses associated with plant spacing variability. “Sixteen percent of the fields had the standard deviation of 3 inches or less. In other words, the study is looking at how far apart the average plants are from the mean of the field — be it 6 or 8 inches — and what is the actual distance that occurs between the plants.
“We're shooting for a standard deviation of 3 inches or less, but that's difficult to achieve. Sixty percent of the fields in the study had a standard deviation of 4 to 5 inches and 24 percent of the fields had a standard deviation of 6 inches or greater. For every inch increase in that plant spacing, grain yield decreased by 2.5 bushels.”
A more recent study, says Lee, from Minnesota, Iowa and Missouri, showed average yield increases where growers repaired and calibrated their planters. This study found that each inch of reduction in the standard deviation increased grain yields by 3 to 4 bushels per acre.
“I would encourage you to calibrate your planters and replace worn parts. You want to aim for as low a standard deviation, or as good a spacing as possible. Before you begin planting, make sure you've done as good a job as possible in calibrating your planter and replacing all worn parts. It's also important that you slow down the speed to manufacturers' recommendations. If you get that spacing as close to perfect as possible, it'll make you money.”
Other causes of planting spacing variability, says Lee, include planter malfunction, incorrect planter adjustments, operator error and excessive planter speed.
The speed of a planter and the bouncing of the row units can interfere with the proper placement of the seed, he says. Seed and soil contact can become irregular, increasing variability in the row, he adds.
Studies also have shown, says Lee, that the strength and direction of wind at planting can have an effect on how and where insecticide granules hit the ground.
Growers should not exceed the planter speed as recommended by the manufacturer, he says. “Studies have shown that grain yields at 6 to 7 miles per hour average about 3 bushels less than the yields of corn planted at 4 to 5 miles per hour. Studies also have shown that these losses due to excessive speed can total $12 to $35 per acre. I'm not sure that 1 to 2 miles per hour extra is worth what it's costing us.”
A planter speed of 6 miles per hour equals 8.8 seeds per second, says Lee. “At a seeding rate of 30,000 seed per acre, that equals a metering rate of 16.2 seeds per second. If you're traveling at 6 miles per hour, that's how many seed you're trying to place in a row per second. Do you think you can place that many seed at equal distances? Just remember that speed kills, and it especially can kill corn yields.”
Another cause of plant spacing variability is death of the plant caused by hail, frost, insects and diseases, says Lee. “Delayed plant emergence can affect yield but not as much as variability. Delayed plants can compete with older, more established plants. It's almost like having a gap.”
Soil-depth control also is important in establishing a good stand of corn, he says. “Seed depth — depending on field conditions — should be no less than 1.5 inches. I've found many problem fields where the seed is one half to three fourths inch deep, and this will cause problems.”
The loss of yield potential in corn production to factors such as plant spacing variability and planting depth, says Lee, can begin as early as day one.
“This loss in yield potential can range from 7 to 15 bushels per acre, and that's a lot of money, especially in this farm economy.”