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Six-row strips boost yield success

Corn harvest conjures up visions of combines pouring golden kernels into an awaiting truck for delivery to the bin.

In reality, there's another harvest occurring from the time corn plants break the soil surface. The plants harvest sunlight that fuels photosynthesis, a process that converts sunlight into vital plant nutrients like sugars.

The more photosynthesis plants generate, the more they thrive. Ultimately, this boosts yields. Finding a way to deliver more sunlight to your plants could increase corn yields.

There is a way

Due to their position in the cornfield, outer rows garner more sunlight. That's what caused Marc Burggraff's yield monitor to jump as the Flandreau, South Dakota, farmer harvested corn on the rows bordering a soybean field four years ago.

“On the six rows on each side of the field, the yield monitor read 20 bushels per acre higher than the rest of the field,” says Burggraff.

This confirmed what Burggraff had read about outside rows yielding more corn due to increased sunlight exposure.

In 2009, he evaluated this on a larger scale by planting intermittent 12-row and 24-row corn strips between matching soybean strips on 90 acres.

Positive results did occur, but not across the entire strip.

“When we weighed the corn row by row, there was only a yield advantage two rows in,” he says. “After that, the yields began plateauing. Yields for the center rows went back to what corn rows normally would be.”

Having more outer rows gave 12-row strips the edge in field-wide tests. In 2009, 12-row strips averaged 195 bushels per acre; 24-row strips averaged 188 bushels per acre.

“We found we gained some yield from 24-row strips. But 12-row strips were a better way to go,” says Burggraff.

In 2010 and 2011, he narrowed strips further to six rows in order to compare them to 12-row strips.

This worked well. In 2010, the average of a six-row strip dwarfed yields of the 12-row strip by over 40 bushels per acre. That was due to the doubling of outside rows in the six-row setup.

In one six-row analysis, outer rows averaged 277 and 291 bushels per acre, respectively. Moving inward, row yields decreased. The innermost two rows garnered 203 and 244 bushels per acre. Another perk was outer rows were 1% drier at harvest. (See chart at right.)

Overall, Burggraff says strips boost corn yields an average 10 to 20 bushels higher than they'd normally be.

Bob Recker, Waterloo, Iowa, noticed the same corn yield bump as he's experimented with strip intercropping. “The edge of the strips is where high productivity lies,” he says.

Ditto for several academic studies' findings. A 1986-1990 Purdue University study showed corn strips with extra population and nitrogen yielded 20 bushels per acre more on average than nonstripped corn (with regular management of that time).

Soybeans shorted

The knock against strip intercropping is the same one that's plagued the practice since it surfaced over two decades ago. Soybean yields take a big hit. The taller corn shadows soybean plants, thus, decreasing the amount of sunlight they garner.

In the Purdue study, stripped soybeans yielded 5.9 bushels per acre less than unstripped soybeans. Nor did strip intercropping boost net profits.

Soybeans also took a hit in Burggraff's on-farm trial. Soybeans in 12-row strips yielded 6 to 8 bushels per acre less than unstripped soybeans.

The soybean slump is a major system flaw, says Emerson Nafziger, University of Illinois Extension agronomist.

“One of my concerns is the general emphasis on high corn yields and the lack of attention on the lowering of soybean yield,” he says. “You can't escape the fact that soybeans always lose to corn in the competition for light and water. And when these are limiting factors, soybeans might lose a lot and even more than corn gains.”

Strips are also too narrow to form a conclusion on how yields really compare against each other.

“In my thinking, that's a flaw. You can say that corn yields were high and soybean yields were not that much lower, but you have no good basis for comparison,” says Nafziger. “It's an interesting topic, but I'm having trouble seeing this as a trend that will sweep the Corn Belt. At the current corn/soybean price ratio, more corn at the expense of soybeans may well make sense. But using strips is only one way – and not logistically a very easy way – to get to more corn in the bin.”


Six-row strips

The soybean-yield hit likely makes 12-row strips a wash when compared with field-wide corn plantings, says Burggraff.

Six-row strips, though, are a different story. In 2010, Burggraff netted an additional $65-per-acre yield return with six-row strips over normally planted corn. It's tough to tally returns from 2011, as a mid-September frost clipped yields from an estimated 55 bushels per acre down to 40-bushel acres in the test field. So far, corn lodging has also not been a problem.

In the future, Burggraff may expand the six-row strips to other fields. Today's technology makes it easier to plant corn and soybeans in strips.

“With 12 rows, I would just skip passes with auto steer and come back and fill in with soybeans on the second pass,” he says. “With six rows, I rigged up my 12-row planter so it would plant the middle six rows to corn and the outside three rows for soybeans.” The system also fits his six-row combine head at harvest.

He applies the same nonselective herbicide to both strip crops with no drift worries. That wasn't the case before Roundup Ready and LibertyLink systems surfaced.

“It's fun to see the yield bump that this has,” he says. “There aren't a lot of products that have this yield kick.”

The emphasis on smaller strips also makes it easier for smaller farmers to adopt. “For smaller producers, it is a way for them to make more money on what they have instead of getting bigger,” says Iowa farmer Recker.

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