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Corn+Soybean Digest

Odd field patterns help identify yield variation at plant level

Think Different Aerial images that show visual patterns in a field can be the first step in discovering problems that affect yields. Follow that up with detailed plant-by-plant analysis on the ground to verify the impact of the problem in yields and more objectively zero in on the problem. Aerial photos early or late in the day produce shadows that point out subtle plant height variations; plant height within a field correlates with ear size and yield. A close look at plant spacing and projected yields from single ears in a 17-foot, 5-inch span (1/1,000 acre in 30-inch rows) vividly shows planter skips and barren plants are yield killers.

When Bob Recker sees odd patterns in cornfields from the air as he flies across farmland in northeastern Iowa, he can’t wait to land and investigate up close. As owner of Cedar Valley Innovation, Waterloo, Iowa, he uses digital and GPS technologies, along with well honed engineering analytical skills to identify yield-loss problems.

Since retiring from Deere, he encourages farmer/clients to “Fail fast, often and cheaply.” There are no failed experiments if you learn from each one, he says. “A farmer is most receptive to change when the data and learning comes from his field, yet most are simply too busy to plan and execute small experiments on their farm,” he says.

Recker schedules his aerial imaging flights for early mornings. “Early mornings produce long shadows that show subtle differences in plant height, and those shorter plants usually signal an impact on yields,” he says. “But you won’t see that yield difference in a combine yield monitor or on a yield map, because they average the yield from a number of plants. You have to get down to the individual plant to really see what is making one plant different from its neighbor.”

Typically, straight-line patterns viewed from the air are manmade.

Recker makes it his business to help farmers figure out variability patterns that signal production problems and yield inconsistencies. “I hand-harvest the ears in a 17-foot, five-inch strip; that equates to 1/1,000 of an acre with 30-inch rows,” he says. “I usually run several replications, and lay the ears at the base of the plants.” The variation in ear size usually intrigues farmer-clients, he says. “Then they want to see the confirmation of what those ears look like on the ground to yields on paper.”

He weighs each ear, and measures plant-to-plant spacing. “I often see a 2:1 difference in yield from the best ear to the worst in the 17-foot span—it’s just amazing,” Recker says. Planter skips or plants that didn’t germinate and barren stalks are all yield killers. “I’ll take a double over a skip any day,” he says. “Plants adjacent to a skip compensate a little, but not a lot.

“I think there’s easily a 10- to 20-bushel an acre improvement there for most operators,” Recker says, “just by making better use of nutrients and seed in the space they have by understanding the variability in a field and being diligent in understanding the root causes of that variability and addressing that in the next season. It’s not something you fix this season, it’s a learning tool to get better next year.


Plant height variation losses

Recker’s client investigations have shown overall good yields on average, but variable emergence, compaction, uneven fertilization and varying seed placement have cut yields overall, often by as much as 20 bushels an acre. “In one instance, a field had a 188-bushel per acre average--that’s not bad. But the single plant variation ranged from 115 bushels an acre to 234 bushels an acre across the planter width,” Recker says. “To me, that says we can do better, if we go to the plant by plant level and determine what caused that inconsistency.”

In one of his investigations this year, Recker noticed plant-height variations on a diagonal pattern across the field as he flew across it. He took photos in early September and the farmer was not surprised at the variation—he had seen streaks in the field from early plant-height variations and even applied twice as much N at sidedress as he had planned to try to even out plant growth.

The farmer had applied manure in mid-April at an angle to the rows when it was really wet. He’d also done some light tillage when the soil was wet, but the tillage was at the opposite angle of the manure application. “The manure-application angle matched the aerial photo, so I figured height variations were related to the manure application. The operator first thought it was some kind of nozzle plugging,” Recker says. “So he told me to go ahead and see what I could find on the ground, even though he didn’t expect to learn a lot.

“He liked the idea that I get right down to the ear, and can pick up a pattern ear by ear. His combine yield monitor told him he gets from 220 to 240 bushels to the acre on this field. But he really understands now that the combine can’t pick up on this individual plant variation—he was surprised to see so much variation in ear size,” Recker says.

They will test further, but the operator no longer thinks it’s a fertilizer issue. “More likely, (the yield hit) is related to compaction of some kind—the pattern seems to match the dual tires of the tractor used for the manure application,” Recker says. “The farmer might consider using tank applicators that drive with the row instead of across it. ”

Recker’s plant-by-plant investigation suggests a lot of potential for higher yields on that field. “It’s yielding well, but it’s crying out for consistent emergence and consistent plant heights that could be producing 300 bushels an acre yields,” Recker says.


Mirrors old Purdue research

Bob Recker’s plant-by-plant findings confirm long-term research by Purdue University that plant-to-plant variability matters in corn yields, especially in no-till continuous corn. A 14-year study there from 1981 to 1994 showed greater plant height variability at week 4, especially in no-till continuous corn, was associated with yield drops. In that study, increases of 23% to 30% variations in plant height were associated with 6-bushel to 41-bushel per acre drops in yield. No-till continuous corn had the greatest plant height variability and lowest yield (see table).

 “We now know that the variation in final plant yield has very little to do with small differences in seedling emergence time or even plant spacing,” says Purdue Agronomy Professor Tony Vyn, who led research in this area.  “Plant-yield variability has a lot more to do with variation in flowering times and stalk diameter near flowering stage. Plant heights are one indicator of a plant’s competitiveness, but stalk diameter and the time between pollen shed and silk emergence is another,” Vyn adds.

            “Another really important story is that plant-to-plant variation really increases with plant stress in the season resulting from things like high plant density or low N fertility. ”

 His research recommends paying close attention to management practices that reduce variability that include 1) distribute residue evenly, 2) avoid soil compaction, 3) place seed with consistent spacing and depth, and 4) apply N precisely and consistently at a safe distance from each plant in the row. For more information see

For more reading on the importance of plant uniformity, see

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