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.”

Ready for action

The planting technology needed to seed variable rates is readily available and being adopted rapidly across the Corn Belt. A majority of new planters purchased in recent years have the hydraulic drives necessary to change seeding rates on the fly. Newer planters and aftermarket drive systems are breaking planters into smaller sections — down to single rows in some cases — for even more refined prescription planting capability. The latest navigation and seed control systems also are up to the task of infinitely altering seeding rates.

Farmers are rapidly testing the waters with these new variable-rate capabilities. A 2009 survey conducted by Pioneer Hi-Bred confirms the rapid adoption of variable-rate seeding. It showed that 20% of Corn Belt farmers with 1,000-plus acres were planting at least some of their acres at variable rates — double the percentage using the practice the previous year. In 2009, more than a third of 1,000-plus-acre farmers owned planters with variable-rate seeding capability, according to the survey.

This rapid acquisition of variable-rate-capable planters is butting up against limited research on how to profitably vary seeding rates. This has some researchers concerned that using the technology too aggressively early on could be a mistake.

Research lags

“Right now we have a theory, a guess, a gut feeling that variable-rate planting should work, but we don’t have the research on how to write a planting prescription,” says Tracy Blackmer, research director for the Iowa Soybean Association. “It is so much easier to develop the equipment than the recommendation to drive it. Right now, variable-rate seeding is guesswork.”

Blackmer notes that most variable-rate seeding recommendations are based on soil map units and aerial imagery. “Soil map units are a very intuitive way to look at how to manage soils differently, but there is not a lot of data on how to draw boundaries. I think there is great potential, but I think it is important to evaluate where it is doing good or hurting you,” he adds.

To that end, the ISA’s On-Farm Network has conducted two years of research on variable seeding rates. Results from the first year’s tests in 2009 raised questions about whether full-field corn seeding rates used by cooperating farmers were too high in the first place. This may have masked potential benefits from variable-rate seeding. Results from 2010 trials were not available at press time.

Nafziger says it makes intuitive sense to vary seeding rates based on yield potential of differing management zones. He has found that corn yields are positively correlated with the plant population needed to produce those yields. So the higher-potential parts of fields should get more seed.

For fields with average variability, corn seeding rates might be set to vary up to 5,000 or 6,000 seeds/acre across the field. Fields with larger ranges of yield potential should see a wider range of rates, but Nafziger says to be careful not to set rates outside the normal range for the growing environment. Except for very light soils, dropping populations to less than about 25,000 seeds/acre may lower yields, especially if weather turns out to be good, he adds.

Illinois research comparing various seeding rates hints at the potential payoff of variable-rate seeding of corn in relatively uniform soils, and in soils with more variability. To simulate variable-rate seeding, researchers compared optimum seeding rates with the most profitable fixed seeding rate.

In northern Illinois, where soils were relatively uniform, the exercise showed an $8.81/acre higher return for the variable rate compared to a 33,500-seed/acre flat rate. In southern Illinois, where soils were more variable, the theoretical return to variable-rate seeding was $34.52 compared to a 27,300 seed/acre flat rate. Higher returns came from avoiding high populations in areas where high populations decreased yields, as well as higher yields from more productive areas with higher-than-normal seeding rates.

The Illinois research mirrors Millar’s experience in central South Dakota, where it is not uncommon to vary seeding rates from 18,000 to 36,000 seeds/acre in the same dryland field. “We absolutely harvest more grain on the low-end areas because we have fewer barren stalks,” he says. “If your yield varies from 75 bu./acre to 220 bu./acre in the same field, it doesn’t take a rocket scientist to see that variable-rate seeding works. But if all you have is a 15- to 20-bu./acre difference, I don’t think you want variable seeding rates.”

Seed company advice

In general, seed companies suggest a go-slow approach when it comes to adopting variable rate seeding. Officials from seed companies interviewed for this story say they are providing information to growers but are not promoting variable-rate seeding as a preferred practice.

“We want to help growers who want to try this technology, but we are not being promotional about it,” says John Chism, North American services implementation manager for Pioneer. “There is not a ton of data out there on variable-rate seeding. That is one of the reasons for our recommendation to try it on a few fields with the most variability. Put your toe in the water. Use some check strips or blocks to make sure it is working for you.”

To help guide variable-rate seeding decisions, Pioneer has published guidelines on its web site and its “Crop Insights” newsletter. To locate them, search “Pioneer variable-rate seeding” with a Web search engine.

Monsanto has conducted planting population and other trials for several years and now is working with its seed partners and farmers as it pilots a prescriptive ag approach. “We know our customers have made investments in variable-rate seeding technology and we want to help them optimize those investments,” says Kyle Freeman, prescriptive agriculture technical manager for Monsanto. “Our goal is to provide population recommendations for our products that they can use to make VRS [variable rate seeding] successful.”

The company, through its seed partners, provides information about appropriate seeding rates for various yield environments. In 2010, Monsanto began a prescription ag solutions pilot program that it will expand in 2011 to provide planting prescriptions on smart data cards to growers interested in variable-rate seeding. The service will be available through select seed dealers as part of its IntelliSeed program. For more information, conduct a Web search for “Monsanto Prescriptive Ag Solutions.”

Mycogen Seeds provides information on how its hybrids and varieties would perform with variable-rate seeding on a one-on-one basis, says Sean Jordal, customer agronomist for parts of Illinois and Indiana. For most customers in his service area, which is dominated by uniform soils, he doesn’t expect much economic benefit from variable-rate seeding.

“Where there isn’t much variability, there probably are more opportunities for growers to capture those last dollars from other management practices than variable-rate seeding,” he says. “I would rather see a grower paying attention to planting the right hybrid at the right population to maximize profitability.”

Monsanto’s Freeman concurs: “If I look at a situation where a farmer has wide variability within fields, there is a significant opportunity. But there probably isn’t much value on flat black soils that are one yield environment.”

Photo courtesy of Kinze Manufacturing