Sunflower & Corn: Rotational Synergy
Perhaps of all crops grown on the Great Plains, sunflower requires the most strategy in choosing its place within a crop rotation.
General university recommendations have pointed toward having a deep-rooted crop like sunflower follow small grain; but some growers are having great success with a different direction — one where sunflower follows corn.
“What we thought, years ago, would never work, has worked and turned out even better than we thought it would,” says retired South Dakota production agronomist and farmer Sam Heikes. “One plus one, it turns out in this case, equals three. It’s that good of a rotation for some growers.”
Heikes worked with a number of growers who favor the corn-sunflower rotation for how it seems to benefit the overall rotational system in terms of yield, particularly in a no-till operation. “It’s about what’s going on around the root systems of the two crops,” Heikes notes. “The relationship is favorable between the microorganisms and fungi unique to each plant species.”
It’s here, underground, where the “secret to success” unfolds. The theory is that what the corn and sunflower root systems have in common complements each other; and what each lacks is filled in by the other.
Don Tanaka, soil scientist with the USDA-ARS Northern Great Plains Research Laboratory at Mandan, N.D., says there’s interaction occurring between the soil, the plants and the water that we don’t fully understand. Corn is one of the highest producers of a beneficial fungus called arbuscular mycorrhizal that facilitates the plants’ uptake of phosphorus. Those fungi also send fungal hyphae — long, branching filamentous structures — out from the root system into the soil, where they create channels in the soil.
The plant is able to interact with the soil profile in a much more extended manner through old root channels. In other words, the corn roots can go after and utilize nutrients and water deeper in the soil profile than with any other crop. Sunflower, after corn, takes advantage of these root channels and follows them to extend further into the soil to find even more nutrients and water.
Larry Nagel, who farms in north central South Dakota, likes the corn-sunflower rotation. The Potter County grower has been in a no-till system for about 15 years. He favors a spring wheat-winter wheat-corn-sunflower rotation on his farm for many different reasons — with most of them revolving around soil health. But ensuring success with this somewhat unconventional rotation requires attention to fertilizer tactics and moisture utilization, as well as weed and disease control.
It starts with the fertilizer right off the bat. “We go in with a high rate of urea, about 150 lbs, in a deep band at planting with our sunflower,” Nagel explains. “We’ve had good luck with our fertilizer going on at seeding. This takes a little more time, but one pass and you’re done.”
The fertilizer package is pretty consistent on the Nagel farm. A starter is applied with the corn, and depending on the year, extra nitrogen may be applied to the winter wheat. Nagel says it makes for a complicated set of hoses on the equipment. But thanks to soil testing each year, they are confident they make the appropriate adjustments to maximize yield for all their crops.
When it comes down to maximizing profitability, Nagel said sunflower continues to be their best cash crop. The rotation and key fertilizer application have allowed the Nagel farm to produce average yields of 1,800 lbs in recent years. That’s actually down a bit from prior years due to the fact that Nagel and his farming partners have been working on newly broken CRP land. Their ’flowers generally average between 2,200-2,500 lbs, with some in the 3,000-lb/ac range in an area of the state known for dry conditions.
How Can It work in Dry Soil?
Some might question how the corn-sunflower rotation would work under normally dry conditions in the Central Plains states. Both corn and sunflower have high water use, so soil moisture is likely to be somewhat depleted after corn (though sunflower has shown the potential to extract subsoil water that is unavailable to other crops).
Nagel likes the benefit from the corn stalks and wheat stubble from two years before that hold in soil moisture for sunflower to use when it needs it later in the season.
South central North Dakota grower Anthony Mock, who farms with his brother Dan in Kidder and Emmons counties, says they favor the wheat-corn-sunflower rotation for both oils and confections —and have for years. Choices are limited in the dry soil areas of North Dakota, and sunflower has proven ideal to utilize every available inch of water. When there is a particularly dry year, sunflower can handle drought stress better than any other crop.
“We’ve done really well with sunflower on our ground in terms of moisture and nutrients,” Mock says. “We’ve had good moisture the last few years; but we also know that won’t be available every year —and sunflower goes deep to get it. Sunflower also goes down to get the leftover nitrogen, especially on the sandy ground that we have.”
The rotation has further advantages in dry areas. Tanaka explains that the soil channels produced by the deep root systems of both corn and sunflower allow water to go deeper into the soil profile, making it less vulnerable to evaporation loss. The rotation is a management tool that not only protects the existing moisture, but can also manage excess water.
Heikes notes that in some years in South Dakota, growers don’t know what to do with all the moisture. “Growers can actually use the corn-sunflower rotation to get rid of excess water,” he explains. “Depending on the winter, the grower can usually count on drier soil in the spring to turn around and get that corn planted in a timely manner, thanks to a deep-rooted crop like sunflower drawing out and using up the moisture the year before.”
With appropriate rotation design, producers can accentuate these positive impacts of sunflower and minimize the adverse effects. Disease impact in sunflower is lowered by a crop interval of three to four years, whereas the synergistic effect of sunflower on yield of following crops is retained. Thanks to rotational strategy and aggressive breeding technology, growers are able to get ahead of disease, insect and weed issues.
“We break up our disease problems [by] rotating broadleaf with grasses,” Nagel says of the corn-sunflower rotation. They deal mainly with downy mildew issues and look specifically for sunflower hybrids resistant to the disease.
The broad spectrum of herbicides used to control weeds in a warm-season grass like corn and a warm-season broadleaf like sunflower covers a lot of different weed species. Weed control is vital for sunflower. Coming in after Roundup Ready® corn is another plus for growers following with sunflower. “You start with a clean field for sunflower, which is so important,” Nagel adds.
Nagel adds even more reasons why they like the rotation. It’s easy to drop the sunflower in between the corn rows, and they look to sunflower roots to break up their heavy soil. “Sunflower mellows that right up,” he points out. That’s also a benefit on CRP land coming back into production.
Mock agrees, saying they like to drop the sunflower in between the old corn rows and it helps break up the corn “trash.”
Tanaka points out that not only does this create an advantage in term of ease of planting; it also has some environmental aspects involved. When sunflower is dropped between the corn rows, the soil tends to be blacker and somewhat warmer, allowing for the sunflower plant to emerge quicker.
Tanaka stresses that a grower must consider key elements when determining the best rotation plan — including what crop was previously on that ground. Since microbial activity is tied to soil temperature and moisture, the microbes naturally are much more active in late May, June and early July. A crop like wheat, barley or canola — all being relatively early maturing — will not make as much use of those nutrients becoming available as will later-maturing crops like sunflower or corn.
Additional breakdown of corn residue will be more gradual, some of which would be cycled into the soil as organic matter and some N that would become available to the following crop late next season as residue decomposition continues. Adequate credit for N contributed by the previous crop should be factored into fertility planning ahead of planting sunflower.
With all these aspects considered, Tanaka says that the number-one factor on whether the corn-sunflower rotation continues to be a success will depend on the available soil moisture. A dynamic system revolves around crop rotation — and for now the corn-sunflower strategy seems to be working. — Sonia Mullally
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