Harvest's Golden Rule
Tuesday, August 1, 2000
filed under: Harvest/Storage
Harvesting sunflower may sometimes be viewed as a delicate balancing act: Harvest too early, and you'll end up with an immature, high-moisture crop, predisposed to diminished yield, lower quality and the likelihood of additional grain drying expenses. Harvest too late, and you'll expose the crop to weathering that degrades seed quality and
lowers economic value, as well as seed yield losses from lodging, shattering and pests.
So when is the right time to harvest?
Most Northern Plains producers gauge their sunflower harvest on a killing frost. But given weather conditions that can vary, along with the production of "stay-green" hybrids, a frost shouldn't always be viewed as the Golden Rule for harvesting 'flowers. Moisture testing is key to avoid harvesting too early or too late.
"Sometimes there's a misconception that you have to have a killing frost before sunflower is ready to harvest. Certainly that is true in many years," says Curt Stern, field representative with ADM's Northern Sun at Enderlin, N.D. "But when we do have warm growing seasons like we're having now, the crop can reach maturity faster, and the heads
seeds are dry. But some producers will drive by the crop and judge it visually and believe it's not ready for harvest. So they wait for that killing frost and then come out and find seeds down in that four- to five-percent range - and then they're losing seed from shelling, along with test weight."
Drydown is quicker and less dependent on frost in more southerly sunflower areas, where warmer temperatures and lower humidity accelerate crop development. "In northern North Dakota, we probably do have to wait for a killing frost to artificially dry that crop down. But south of I-94 and especially getting into South Dakota, the crop can come along fast - and that's where the stay-green gene particularly has the potential to fool producers," says Stern, a 30-year veteran of the sunflower industry. Stern thinks a good harvest range is 10- to 15-percent moisture. He believes it can be more economical to artificially dry a crop that's close to 15 percent moisture than to risk increased shelling once the standing crop falls below 10 percent.
"I think that's even more true with confections, because you have a much bigger, plumper seed; so the seeds don't pack as tight in the head, and the shelling potential increases compared to oil sunflower," he adds.
Stern points out that if the crop gets too dry and you find 10 seeds on the ground per square foot, that's a loss of 100 pounds per acre. "We found [instances of] 20 to 30 seeds per square foot, even as early as September, three years ago. The losses can add up in a hurry.
"I think the message would be to get out and check the crop moisture - especially if it's a warm fall with low humidity," Stern concludes. "It's as simple as running out there and rubbing a few seeds out of the head and getting a moisture test."
High Plains Moisture Testing
A killing frost isn't needed in drier, warmer sunflower-producing areas like Kansas and Colorado. Still, moisture testing is recommended by many to gauge harvest timeliness.
"Sometimes it can be tough to determine when to harvest. You can sample at 14- to 15-percent moisture, wait a day or two - and then it'll be too dry," says Mike Bretz, crop production director for Sigco Sun Products, Goodland, Kan. When testing a sample, be sure to take into account the potential moisture differences between the hull and the inside kernel, Bretz advises. A moisture meter can be fooled by sunflower with hulls that are drier than the kernels inside. "Cut a test sample and put it in a coffee can; then leave it a few hours or overnight for a more accurate moisture reading," he says.
Sunflower harvested too dry will be prone to shattering. Also, it's more difficult to separate foreign material from the seeds. And sunflower that is harvested too wet might not be accepted by some grain elevators in the High Plains, where grain drying capacity is limited.
"For most elevators around here, sunflower needs to be around no more than 10 to 12 percent before it's even a deliverable commodity," says Lynn Hoelting, general manager of Mueller Grain Company, Goodland. "We start discounting above 10 percent, although we'll receive 12-percent moisture sunflower, [as will] most places."
Hoelting says most producers in the High Plains wait for sunflower to dry down naturally to below 12-percent moisture before harvesting. "And that's usually not a problem, because in most years we don't have adverse weather conditions in the fall."
Sampling is recommended before harvesting sunflower which is too wet. However, refrain from harvesting too much before sampling. "Don't go out and do a test cut of a semi load with 17-percent moisture, because that's a problem," Hoelting states. "The elevator may not receive it down here; and, in fact, might not even have the drying capacity to do it."
NDSU Study of Harvest Date Influence
Burton Johnson, a sunflower researcher at North Dakota State University, has been studying the influence of harvest date on sunflower performance since 1998. Four locations are included in the study: Carrington, Hettinger and Prosper (near Fargo) in North Dakota, as well as one at Brookings, S.D. A site near Minot, N.D., was added this year. Selected sites are purposely not in areas with heavy blackbird pressure.
Commercial oil-type hybrids in the study are Cargill 187, Interstate 6111 and Pioneer 6338, which are representative of early, average and late maturity, respectively. These hybrids also represent diversity in their expression of the stay-green trait, with I6111 not exhibiting the trait, C187 having slight trait expression, and P6338 considered to be a
stay-green hybrid. (The stay-green hybrid was not included in the first year of the study.)
The study's initial harvest date is scheduled to begin when seed moisture is between 25-30 percent. The study has four subsequent harvest dates at approximate nine-day intervals. Thus, harvest spans from 35 to 40 days from the first to last date at each test site.
Performance results have varied by environmental conditions at each of the sites. What Johnson's study has determined thus far is that quite often (but not always), a yield loss will coincide with delayed harvest. Of the combined test site results from 1998 and 1999, six of eight sites experienced a reduction in yield from delayed harvest. The losses - whether it was seeds, part of the head, or the entire plant - were due to a variety of causes, including lodging, seed shattering caused by head rot, insect damage and bird damage.
"When you plant impacts when you harvest, along with weather conditions," Johnson points out. "But the longer we delay harvest, the greater the risk for yield loss and crop deterioration."
More-complete delayed harvest data will be available after Johnson concludes the third and final year of the study this fall.
Johnson is conducting a related study on sunflower desiccation and plant drydown, comparing plant moisture losses from conventional and stay-green hybrids.
The first year of the three-year study was conducted in 1999 at Carrington and Prosper, N.D. Conventional oilseed hybrids in the study are Cargill 187 and Pioneer 63M91. Stay-green hybrids are Pioneer 6338 and a nonoil hybrid, "Bigfoot" from Seeds 2000.
Slower crop development due to below-average temperatures in August and September of 1999, coupled with the arrival of a killing frost before desiccant application, affected the first year's evaluation of chemical desiccation. But Johnson was still able to compare plant moisture of the conventional and stay-green hybrids at physiological maturity and subsequent moisture sampling dates. In that initial season, stay-green and conventional hybrids exhibited similar seed moisture levels across moisture sampling dates. Stalk moisture levels varied. However, receptacle moisture levels were greater
for stay-green than conventional hybrids for a given seed moisture level. High receptacle moisture causes threshing difficulties by plugging the combine.
While stay-green hybrids offer better late-season plant health and potentially greater yield due to less impact from pests and lodging, growers need to monitor seed moisture closely with stay-green hybrids, since plant color change isn't necessarily an indicator of seed moisture content. - Tracy Sayler