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Computer signals corn planter just how much seed to drop

On cold days last winter when his son hauled grain, Dennis Carnahan was content to sit at the desk and work on the computer. What he accomplished was just as productive as putting in manual labor.

“I enjoy working on the computer,” Dennis says. He farms with his brother, Ross, and son, John, near Vincennes. “Driving a truck isn’t something I enjoy. I would much rather build prescription planting maps for this spring.”

With spring here, whenever their planter or air seeder runs, the format Dennis created weeks ago will tell the corn planter or air seeder how much seed to drop at any one spot in the field. The Carnahans farm lots of rolling land with varying soil types. They are big believers in varying seeding rate to match soil types.

Key Points

Higher corn rates are reserved for the most productive soils.

The highest soybean seeding rates are used on the lightest soils.

Dennis Carnahan builds his prescription planting maps on a computer.


“We use yield information from combine monitors, but I don’t even print out the maps most of the time,” Dennis says. “When I sit here and prepare my prescription seeding map instructions, it’s strictly based on the soils types in each field, as gleaned primarily from soil maps.”

Twist on rates

Your first reaction might be that if you want to raise more crops, you need to bump up the rate on better soils and drop the rate on lower soils. That works for corn in the Carnahans’ case, but not soybeans.

“We stay in a pretty narrow range on regular corn,” Dennis says. He notes that Ross plants the corn and prefers a narrow range. “We usually vary from 27,000 to 30,000 kernels per acre.

“For corn we program the highest seeding rate on the best ground. Then we drop the rate slightly on more rolling ground. So we have the thickest populations on our best soils for corn.”

In soybeans, the situation is reversed, he adds. Typical seeding rates for soybeans vary from about 140,000 up to 180,000 to 200,000 on higher ground. Too-high rates on the most productive soils can lead to lodging and could actually result in less yield, Dennis says.

“It may seem backwards to some people, but it works for us,” Dennis says. “Those better soils can handle corn, and corn yield comes from more population. But sometimes soybeans aren’t as productive if they’re too thick.”

Most air seeders are set up on 7.5-inch rows. However, the air drill that the Carnahans use is set on a 10-inch row spacing.

Invest in technology

The Carnahans believe in keeping precision technology up to date. They’ve recently upgraded their system to accommodate the latest version of John Deere’s Greenstar system, Greenstar III. It’s billed as having the capability to work with the most up-to-date satellites.

“Autosteer is a plus,” Dennis says. “We don’t need markers. In fact we’ve never used foam markers. But with the guidance options we have today, we can stay on course and do a good job.”

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Adjust on the go: Matching seeding rates to soil types is important for Dennis Carnahan and his son, John.

This article published in the May, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.