Farm Progress

Farming on The Edge | Strip Intercropping Edges Capture More Light, Reward With Higher YieldsFarming on The Edge | Strip Intercropping Edges Capture More Light, Reward With Higher Yields

Susan Winsor

October 14, 2011

10 Min Read


How can we translate “farming smarter” and technology into an extra 40 bu.? Fasten your seatbelts for a tour of what may be the future of corn and bean farming.

Strip intercropping leverages sunlight, guidance technology and sometimes variable-rate planting to average roughly 290-bu./acre corn, according to several years’ research by curious growers in Iowa, South Dakota and Minnesota. Their alternating swaths range from four to 12 rows wide, with various row widths.

In Flandreau, SD, strip-intercropper Marc Burggraff has seen up to a 100-bu./acre difference between the outside corn row (of six-row corn strips) and the middle corn row of his strips. A few of his outside corn rows exceeded 290 bu./acre in 2010. He tested both 12-row and six-row strips of corn/soybeans in 2010.

“My six-row corn strips averaged 235 bu./acre, with two of them going over 250 bu./acre. This is amazing since our county average is in the 160s,” Burggraffsays. “A whole field of my mono-crop corn would average around 200 bu./acre in that field.” 

He does not vary corn-row populations by location, and rotates between Roundup Ready and Liberty Link genetics.

“My 12-row strips right beside the six’s yielded 215 bu./acre,” he says, compared to the whole field of 2010 (mono-crop) corn yield of 200 bu./acre. “It was amazing to see those numbers,” Burggraff says.

He’s experimented with strip intercropping for six years, expanding to 45 and then 90 acres. He first tried strip intercropping in 2006 after reading online ag forum strip-intercropping results from Clay Mitchell, Buckingham, Iowa, and Iowa’s Bob Recker.

Burggraff is the buzz at the local coffee shop because he plants two crops on the same pass with variable-rate electronic controls on a White 12-row planter. “I plant three rows of beans on the outside rows, and six rows of corn in the middle, effectively making six-row strips,” he says.

In southern Minnesota, “strips are the most profitable ground I farm, says southern Minnesota grower and engineer Sheldon Stevermer from Wells. “My (2010) strip intercrop had a net return of $120/acre over all soybeans. This is based on a strip-intercrop corn yield average of 231 bu./acre,” he says. “I have never combined corn with stalks that thick, like trees,” Stevermer says.

 “This fall’s corn yield was about 5 bu. better than the three-year corn average (of continuous corn),” he says. “I think it’s possible to get 30-40-bu./acre better corn yields if the right hybrid’s planted. Some hybrids respond significantly better than others in this environment. The hybrid we planted this year just didn’t have the large ears on the outside rows.

 “The beans were a few bushels better than our 2011 farm average. Given that the field’s been in continuous corn, I’d have expected the bean yields to be better. However, we did plant a group 2.3 bean there, and the mid-September frost did nail them rather hard, especially the green ones. I think hybrid and variety selection is key in optimizing yield with strip intercrop.”

This year, he devoted 80 acres to strip intercropping.

So why the bump in yields? When corn grows along the edge of a field, the outside rows respond disproportionately well to extra sunlight (see sidebar). By boosting the corn plant populations of these sunniest outside rows to leverage the extra light reaching them, Bob Recker sees corn yields of 348 bu. in that outside row, gradually tapering off in relation to distance from the edge. Recker is a retired John Deere engineer and owns Cedar Valley Innovation, Waterloo, IA.

He’s tested strip intercropping across nine sites in east-central Iowa over five years. Not all strip intercroppers vary corn populations by row, but they still realize worthwhile gains.

Either way, Recker likens strip intercropping to “a roadster that performs extremely well on a good road, but not rough ground or muddy lanes. It’s not a panacea unless you’re paying attention. But it is a consistent way, especially with the variable-rate planting, of taking some giant strides in corn yields.”

He scrutinizes inter-plant spacing, grain yield per plant and other agronomic variables of strip intercropping to tailor the microclimate that teases out every last kernel from each plant.

Creating artificial field edges and outside rows is also a fascination for Roger Knutson, Hubbard, IA, and his son-in-law, ag engineer Jacob Bolson. Collaborating with Recker, they’ve concluded that “you need eight or fewer rows per strip to maximize the outside-row effect,” Knutson says.

In 2010, he evaluated a set of four-row strips, with the outer two corn rows planted at 56,000/acre and inner two rows planted at 28,000. For 2011, he plans to evaluate strips at an even higher population.

 “Once you take strip intercropping to a production scale, RTK guidance is key to optimize nutrient placement and residue management from year to year,” Bolson says.

“Strip intercropping also offers a huge opportunity to introduce controlled traffic to reduce compaction,” he adds. Controlled traffic was the focus of his graduate research.

Recker’s brother Herb and nephew Mike have tested strips for three years on their home farm near Dyersville, IA, where they operate a seed dealership. Alternating six-row strips of corn/beans, they gained an average of 40 bu./acre on their corn, with “edge-row” corn yields as high as 325 bu./acre on ground “that has to stretch to reach 200 in monocrop,” Bob says. The Reckers bumped plant populations on the outside corn row to 62,000/acre. The second row in from the edge is planted at 52,000, and the third row is at 36,000.

“Equipment-wise, the biggest challenge was coming up with a six-row bean (combine) head, but if I make an extra $160/acre, I’m pretty motivated,” Herb admits.

Variable-rate planting generally increases the outside-row sunlight effect, but is not a requirement to capture its benefit.

The Reckers note that they did not lodge during the July high-wind event in east-central Iowa. “Of course hybrid selection is key, but we dispelled the conventional wisdom of higher populations lodging from those 65-mph winds,” Mike says.

 “It makes sense that it didn’t lodge because the outer plants are not resource-limited due to neighbor competition since they are instead dominating over the soybean,” says Iowa State University’s Lori Abendroth, project manager, climate and sustainable corn-based systems. “Lodging and high populations only go together, typically, when plants are resource-limited in some way.”

Strip intercropping today “reminds me of GPS when I first evaluated it in 1992,” says ECI Co-op Agronomy Manager Gene Mitchell, Hudson, IA. “It was pretty Star Wars. But the software has evolved, and the data we now get from it is really useful. If we’re going to double our crop production by 2030, this might be a concept to consider.It probably doesn’t lend itself well to a 20,000-acre grower with a 48-row planter right now; it’s going to be an early adopter who thinks out of the box,” Mitchell says.


Leverage your light

When corn grows along a field edge or a shorter neighboring crop, the outside two rows respond especially well to extra sunlight. Corn (a C4 plant, like sugarcane and pineapple) is more photosynthetically efficient than most plants (C3 plants). Soybeans have less to lose from taller neighboring corn plant shadows than do other corn plants.

Strip intercropping creates more light-saturated corn outside rows by alternating swaths of shorter crops (like soybeans, small grains, perennial grasses or specialty crops) with corn swaths. Those with variable-rate planters can boost outside-row corn populations to 60,000/acre (5 in. between plants in 20-in. rows), and scale back proportionately in rows further from the edge.

This further leverages the extra sunlight those outside rows to deliver up to 400 bu./acre corn yield in that single outside row, according to research led by Bob Recker, Cedar Valley Innovation, Waterloo, IA, in collaboration with local growers.

The second row in from the edge has responded with roughly 281-bu./acre corn yields.

Typically a grower who tries six-row-wide strips at normal populations would see outer-row-only yield equivalents of about 290 bu./acre corn, Recker says. If he bumps his outer-row population to 50,000, he should see roughly the equivalent of a 350-bu./acre yield in that outer row alone, Recker says.

Soybean yields often suffer 10-15% yield hits when grown in strips, although a number of growers featured here have overcome that, Recker says.

Ben Witte, Fairbank, IA, for example, has average bean yields in his strips of 56.7 bu. by using a proven Group 3.1 disease-tolerant, fungicide- and insecticide-treated variety, planted at 152,000/acre.


Mixed academic assessment

“It would not surprise me, in a short period of time, to drive down the road and see corn and soybeans planted in strips,” says University of Illinois Ag Economist David Bullock after evaluating two years of strip-intercropping data. He evaluated about three football fields’ worth of experimental strips planted in eight-row swaths (30-in. rows). He and two colleagues will be publishing a full evaluation soon, he says. “What we see is very encouraging.”

Don Bullock, the study’s University of Illinois ag statistician, says the increased revenue could be as high as $80-90/acre when corn is $5-6 and beans around $13 and you use higher seeding rates.”

Roger Elmore, Iowa State University corn agronomist, summarizes strips’ tradeoffs as he sees them: “Our limited work with these kinds of systems in Nebraska indicates that although the outer rows of corn had increased yields and the inner rows lower, soybean yields responded in the opposite way. So it will come down to how much you’ll gain in corn vs. how much you’ll lose in soybeans, plus the economics of corn vs. bean prices. Management, too, is more difficult, at least if herbicide mode of actions are rotated, etc.”

Twelve years ago, a strip-intercropping assessment by Iowa State University Agronomist Richard Cruse called strip intercropping too management-intensive. That was in 1999, before guidance technology, variable-rate planting and glyphosate resistance.

Today, Cruse dismisses strip intercropping for the average grower for “reasons of scale. It restricts the number of acres you can farm,” he says. “Growers these days focus on large expanses of land, rather than adding more bushels per-acre on smaller tracts.”

Not so, says 140-acre Fairbank, IA, farmer and retired John Deere Engineer Ben Witte. “The most capital-efficient profits originate from multiplying yields on existing ground, rather than adding new acres to cover,” he says.

This logic of higher profits and fewer acres also makes sense to Herb Recker, a three-year strip-intercrop veteran and longtime seed dealer in Dyersville, IA. “Strip intercropping could be one way for beginning farmers to become more efficient without adding acres. A young farmer with a good deal on a 12-row planter would save big money on his power needs no-tilling corn in bean stubble and moving six rows over each year,” he says.

Overall, “in my mind, the system is plausible but requires greater management and attention to detail since the crops grow at different rates and require different management inputs,” says Iowa State University’s Lori Abendroth, project manager, climate and sustainable corn-based systems. “The concept of higher yields on the outer rows of corn makes perfect sense.”


Try a sunlight portal

Do your own on-farm test and create a single sunlight portal midfield to assess strip intercropping on your operation, suggests Bob Recker, owner of Cedar Valley Innovation, a Waterloo, IA, and strip-intercropping enthusiast.

Deliberate fallow rectangles in the middle of a cornfield are one way to document the yield boost of added sunlight on corn. Such “sunlight portals” –measuring one row to four rows wide – have boosted single-row corn yields as high as 280 bu./acre, says Recker.

By increasing single-row populations up to the equivalent of 60,000/acre, corn-portal-facing single-row yields have topped 380 bu./acre, compared to 270 bu. on the next row away from the edge, according to Recker’s portal studies.

 He calculates these acre-equivalent yields in the single row facing the sunlight portal, and extrapolates the data to meaningful per-acre yield figures. 

About the Author(s)

Susan Winsor

Before joining Corn and Soybean Digest, Susan was an agricultural magazine editor for Miller Publishing, a newspaper reporter for Gannett newspapers and Manager, Marketing Publications for Cenex/Land O’Lakes Ag Services. She graduated from Colorado State University with a Bachelor of Science degree in Agricultural Journalism.

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