Optimum population rate swings stymie the potential of variable rate planting. Yet, improved data collection may one day aid this promising technology.

The good news is that variable rate technology may simply be ahead of its time.

Variable rate seeding may prompt you to swap your seed corn cap for a chef's hat. A pinch of seed on low-producing soil, followed by a dash on medium-producing ground and a heaping helping on highly productive river-bottom land should yield a bumper crop. That's because this meticulous mix matches optimum populations with correct soil types.

Well, maybe.

If a field greatly differs in yield potential, varying corn populations for specific soils certainly makes sense. “Corners of center-pivot irrigation systems are good examples,” says Emerson Nafziger, University of Illinois extension agronomist. “Because you can't irrigate them, you know you won't get high yields on the corners.”

But it's a different story on other Corn Belt fields, Nafziger says. Many industry and university studies show that the cost of variable rate seeding equipment and software — which can tally up to $5,000 — may dwarf the economic benefit of any yield gains.

“It can be so costly and time-consuming to know what the variable rate should be for each part of the field that one can't afford to do it,” Nafziger says. “As a guess, we think that yields within a field would need to vary by 50% in order to make it pay.”

Tough to track

The merits of variable rate planting are hazy because the best planting rates differ from year to year. Corn Belt data collected by Pioneer Hi-Bred International researchers over four to six years reveal that optimum plant populations for specific field areas may vary from 22,000 plants per acre (ppa) to 34,000 ppa.

“You'd think that a portion of a field would have the same optimum plant population year in and year out,” says Tom Doerge, an agronomy research manager for Pioneer. “But huge differences can occur.”

Environmental conditions, including rainfall and temperature, can greatly affect optimum populations. Although top-notch seed corn normally has a 95% germination rate, University of Missouri researchers found germination rates varied between 50 to 95% in variable rate trials.

“Early, heavy rains resulted in poor germination, poor stands and a poor economic payback,” says Glenn Davis, university agronomist. “For Missouri conditions, we found that we need to have a better handle on predicting the weather and plant survival before we can hope to make sense out of variable rate planting.”

Such studies have dashed the initial belief that variable rate seeding could bag big bucks for farmers.

“It makes perfect sense that you should cut back on inputs where you don't need them,” Doerge says. “But you don't know where you need high and low seeding rates each year. You can't capture the value every year by looking into the future and predicting what kind of weather year you will have.”

Breeding bias

The industry's plant breeding strategy also is biased against variable rate seeding. “Corn hybrids are designed to be planted under a specific population across an entire field, rather than different rates across areas of a field,” says Sean Jordal, accounts manager for Mycogen Seeds.

That's why Pioneer now recommends 26,000 to 30,000 ppa for a Corn Belt harvesttime population, Doerge says. This range helps ensure sufficient populations for all field areas in good and bad years.

“I'd never tell someone that this is a year where they could get away with planting 22,000 plants per acre,” Doerge says. “They may save money on seed, but they could lose more money in yield.”

Variable rate seeding may have more potential under lighter soils and arid climates, Jordal says. “A 2% yield increase will show up more if you typically grow 120 to 130 bu./acre corn, compared to 190 bu.,” he adds.

A 1996-99 study conducted on the outer fringe of the Corn Belt at Colorado State University (CSU) showed that variable rate seeding indeed has potential on variable soils. Still, researchers experienced the same challenge that their Corn Belt colleagues faced.

“Even in a traditional low-producing area, you don't want to back off the plant population in case it rains that year,” says John Shanahan, a USDA-ARS research agronomist who previously worked at CSU on the study. “When you push the populations, you don't see a loss in yield if you plant over the optimum rate. But if you don't plant enough seeds, you will see a yield decrease if you have good growing conditions.”

Niche markets

Although variable rate seeding doesn't fit mainstream use, it works well in niches such as center pivot corners.

“Rather than plant these areas separately at a reduced rate, farmers like to keep planting the whole field,” says Jerry Schmitt, general marketing manager for AGCO's Fieldstar precision agriculture program.

AGCO's differential GPS variable rate controller automatically switches rates on the go. This saves farmers the downtime they would endure by changing their planter's population rates. The automated system also enables farmers to plant different rates at night, when difficulties in discerning the border between irrigated land and corners arise, Schmitt says.

End rows and land near fences and trees also tend to be less productive than the rest of the field, says Bob Rauh, product information manager for the John Deere Seeding Division.

It gets better

The good news is that variable rate technology may simply be ahead of its time. David and Donald Bullock, two brothers who are a University of Illinois agricultural economist and a crop scientist, respectively, studied how farmers use soil productivity information to form variable seeding rates. Pioneer and Deere sponsored the study.

“The field information and the technology are what we call economic complements,” David says. “The more information you have, the more valuable the technology; the more technology you have, the more valuable the information.”

Soil productivity information that farmers glean from yield monitors reveals little about optimum seeding rates for field regions, David says. However, advances in automatic soil sampling and satellite photography could snare more precise seeding rates.

“The key is obtaining information cheaply,” David says. “Once that becomes a reality, the variable rate application technology may become profitable for farmers.”

Industry has already improved variable rate technology. In 1999, AGCO introduced its Fieldstar system that enables farmers to write their seeding plans on computer software. All of AGCO's White hydraulic planters have been available with a factory-installed GPS variable rate controller since 1999.

Later this year, Deere will follow suit by introducing desktop software in which a farmer can use information from yield maps and/or soil type maps to develop a personalized seeding prescription plan. With the exception of its 1780 model, Deere markets each of its 1700 series planters with a variable rate drive.

David Bullock reminds producers that variable rate technology is not flash-in-the-pan science. “But it will require changes in the way we get information to make it profitable for farmers,” he says. “We expect firms will be working hard to find cheaper ways to obtain the necessary information.”

Specific seeding

When he's planting, Dennis Lindsay must feel as if he's elk hunting with a shotgun filled with pheasant shells. The Masonville, IA, farmer and his two sons would rather use a “rifle” approach and more precisely match hybrids or varieties with particular field areas. They have designed a planter and purchased accompanying software that changes seed type while planting.

“We have proved the planter will work,” Lindsay says. “But the real challenge is getting information from seed companies about specific areas where specific varieties work best.”

Uneven results

Seed companies don't intentionally slight variety or hybrid selection for variable seeding, says Tom Doerge, agronomy research manager for Pioneer Hi-Bred International. However, neither seed companies nor scientists know enough to make variable planting work consistently.

“Certainly, there is great agronomic appeal for varying hybrids and varieties in a field to match differences in the environment,” Doerge says. “Unfortunately, the year-to-year variation is tremendous. One year a variety can be the top yielder and the poorest yielder the next year.”

That's why seed companies use a wide-reaching “shotgun” development approach. Rather than specifically breed varieties and hybrids for certain conditions, such as wet weather, firms design them to thrive over a wide range of conditions.

Some industry and university trials back the merits of variable planting. In a 1997-98 variable rate study by Case Corporation, corn hybrids showed a 5 to 15 bu./acre yield advantage when researchers matched specific hybrids with specific soil types.

Iowa State University researchers also found that variable variety seeding boosted soybean yields on soils plagued with iron chlorosis. Researchers used yield monitor values to develop a yield difference map. An analysis showed that, in some areas, an iron-chlorosis-tolerant variety outyielded an iron-chlorosis-susceptible variety by 7 to 20 bu./acre.

Case discontinued the trial after 1998 before researchers could determine if the increased profit paid for the experimental Case-IH Cyclo planter. Meanwhile, ISU researchers wonder about their trial's consistency. In some iron-chlorosis-plagued areas, the susceptible variety outyielded the tolerant one, says Dale Farnham, an ISU extension agronomist.

“Although site-specific placement of varieties may be beneficial in some cases, it seems to be unpredictable,” he concludes.

Refuge role

A niche market may someday exist for variable seed planters, says Darian Landolt, site assessment researcher for Case-New Holland.

“I think they could work for creating Bt refuges that reside in different areas of a field, rather than one solid block,” he says. “That way, you could give up corn yields with the Bt refuge corn without sacrificing good ground.”

But unless seed companies breed more for specific traits, variable seed planting likely won't progress.

“Hybrids are developed to do well over a wide range of conditions, so it can be difficult to find out whether Hybrid A or Hybrid B will do best in a certain part of the field,” says Emerson Nafziger, University of Illinois extension agronomist. “A better and less costly option is to spread the risk across your farm by planting a number of hybrids across different fields.”