Interest in double cropping this coming planting season should be strong, as commodity prices call for more acres of all crops and farmers look to maximize their income opportunities.
The planting window for most second crops is quite narrow. However, research conducted at Oklahoma State University by agronomist Chad Godsey reveals that the window for sunflower is quite wide. Godsey has been researching sunflower planting dates at two Oklahoma locations in Stillwater and Lahoma. His work was financially supported by the National Sunflower Association.
For maximizing potential yield, Godsey’s research points to a late June or July planting date as being ideal for double cropping sunflower in most of Oklahoma. Even planting in the last week in July provides enough time for the crop to mature prior to the first hard freeze.
When planting sunflower as a spring crop, Godsey recommends an April seeding date for the best potential yield. But he sees sunflower after winter wheat to be a very good fit for Oklahoma farmers. He stresses that second-crop management has to be part of a farmer’s plan if good management is part of that plan overall.
The first management decision is the use of herbicides in wheat. Godsey says that a lot of sulfonylurea (SU) herbicides are used to control weeds in winter wheat, so careful attention needs to be made to avoid carryover damage on sunflower.
PowerFlex® is a common herbicide used by Oklahoma farmers in October and November. The product label has a nine-month plant-back requirement, so a late June/July sunflower planting date is right at the limit.
An acceptable common spring herbicide is Harmony® Extra, which has a 45-day plant-back requirement. Most spring applications are made in early March, so a late June sunflower planting is well within the label requirement.
Other products may have a tighter restriction for plant-back. If a farmer has good soil moisture after his wheat harvest, it is important that he not be locked out of a second-crop opportunity because of the herbicides he used earlier. It will be a matter of checking labels for rotation restrictions. So it is important to do the early planning now to take advantage of a second crop that can generate an additional $300 to $400 per acre.
When double-cropping sunflower, Godsey says a preplant burndown is a must. He recommends a glyphosate product. Spartan is his choice for season-long weed control. “I recommend adding Prowl H20 when sunflower is the first crop. But when double cropping in heavy residue, the Prowl may not be adding a lot of protection and could be dropped,” the OSU agronomist advises. Weed pressure tends to decrease this late in the growing season, he points out, so getting a good preplant kill is mandatory.
Tillage is quite common in much of Oklahoma. But when double cropping after winter wheat, Godsey is a stickler on planting the seeds right into the wheat stubble. “In this region, we can dry out the soil very quickly in July and August. A tillage one to two days prior to planting would really dry out the topsoil to the point where emergence could be a concern,” he says. Getting a good stand with equidistant plant spacing is a key to a successful crop. So planting into moisture is critical.
Godsey suggests a seeding rate between 18,000 to 22,000 seeds per acre, moving from west to east in the state, respectively. Sunflower offers a significant viable range for populations and still maintain above-average yields.
An issue of concern is fertility. Often times, a second crop is treated as a “scavenger,” resulting in disappointing yields. “If you are going to the expense of buying seed, controlling weeds and planting the crop, why would you skimp of fertility?” Godsey asks. It is well known that sunflower can go deep for residual nutrients. Soil testing is obviously the best way to find out what is left in the soil; and when double cropping, that may not always be possible due to time constraints. Nitrogen is the most important nutrient for sunflower, with the general rule being 50 lbs/N per 1,000 lbs of expected yield.
Past soil tests will be a good indicator of phosphorus (P) and potassium (K). If the field has a history of low P, such as from 0 to 7 parts per million (ppm), then 20 to 30 lbs/P per 1,000 lbs expected yield is recommended. Levels above 16 ppm do not need additional P. For K, the recommendation is much the same. If prior soil tests indicate from 40 to 80 ppm, then from 40 to 50 lbs of K is recommended per 1,000 lbs of expected yield. Soils with 120 to 160 lbs/ac of K do not need a supplemental treatment.
The High Plains Sunflower Production Handbook is a good fertility resource. This publication can be found on the National Sunflower Association’s website under the “Growers” section.
Nitrogen should be applied below the soil surface if possible since this would likely reduce N loss through volatilization. The majority of surface-applied N can be lost if applied on a warm and windy day during the summer. Phosphorus and potassium should be applied prior to planting and possibly just prior to wheat planting the prior fall. This cuts one application pass.
Of concern to at least one part of the High Plains — southern Kansas and much of Oklahoma — is low soil pH. Levels of soil pH under 5.5 can result in disappointing yields, according to Godsey. “When you have pH levels below 5.5, applying lime at or right before planting is not going to do much, so a producer has to really consider if planting a second crop like sunflower is worth it. Most likely you would not have a crop failure, but yields could be reduced,” he states.
One of the advantages of a late June or even later planting is the absence of head moth. “We have not seen head moth after our mid-June planting date,” Godsey indicates. However, scouting still will be important since this insect has been unpredictable over the years.
What to crop following sunflower? Godsey says it still may be possible to plant winter wheat in the fall; but his recommendation is to follow sunflower with an early spring crop like soybean, grain sorghum or corn.
So what is the advantage of putting in a second crop like sunflower? Obviously one reason is the potential for good returns — which doesn’t happen every year. Godsey likes sunflower in an extended rotation due to the deep-rooted nature of the plant. He also likes the use of a different mode of action in weed control, which is obviously important in resistance management. Sunflower is a crop that allows producers in the region to diversify and intensify their rotations.
— Larry Kleingartner
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