As planters capable of varying seeding rates on the go become more common, researchers and seed company agronomists are coming to grips with where prescription planting has the most value — and where it offers less potential.

In a nutshell, here’s their advice: Give variable-rate seeding a whirl, if you’ve got the itch to find how it works in your operation. But proceed with caution on a small percentage of your acres. Focus first on corn, not soybeans, since the return for corn is thought to be greater. And choose fields with the most variability, since that’s where the practice seems to have the biggest payoff.

Like many precision ag technologies, variable-rate seeding seems to offer plenty of promise. Just the right amount of any input in the right place should maximize efficiency, right?But higher profits from more yield, lower seed costs, or both, aren’t a sure thing.

“The big factor that drives variable-rate seeding performance is soil variability,” says Jim Millar of Precision Soil Management, Redfield, SD, many of whose customers have boosted yields and profits through precision seeding. “Soil variability really displays itself under less-than-ideal growing conditions like we have in central South Dakota. Under those conditions, variable-rate seeding really pays for itself.”

But farmers with relatively uniform soils typical of the central Corn Belt shouldn’t expect a big productivity boost from variable-rate seeding, says Emerson Nafziger, University of Illinois Extension agronomist.

“I’m generally supportive of variable-rate seeding, but doubt that it is going to make people lots of money in many fields,” Nafziger says. “Except in highly variable fields, I see a relatively low payoff, but also a relatively low cost of using the technology. We have a lot of fields in Illinois where we don’t have a huge range of variability, so varying seeding rates isn’t going to offer very much for many farmers. But there’s little downside, and it certainly can help people think about their fields and how they manage crops.”