June 1998
Estimating early season yield potential
"Spring Wheat Doc" uses spike exams to forecast bushels
By Tracy Sayler
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Prairie Grains is the
official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain
Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.
It's early in the growing season, but Dr. Ed Vasey says the yield potential of your wheat crop can already be estimated quite accurately.
Vasey is a retired North Dakota State University extension soils and cropping systems specialist. Along with business partner Lee Mayer, he now runs a crop consulting firm, Spring Wheat Doctor Inc. of Fargo.
Wheat develops in a systematic pattern correlated to air temperature or growing degree days (GDD), says Vasey. With the knowledge of a producer's planting date, weather data, and weather forecasts (the latter Vasey receives in an agreement with Meridian Environmental Technologies Inc., Grand Forks, ND) GDD can be used to track wheat stage development, with adjustments for variety and seedbed conditions. Timely windows for herbicide applications, treating pests such as scab and the orange wheat blossom midge, and top-dressing nitrogen to enhance wheat protein can thus be determined.
Offering a crop staging report and crop management prescriptions during the growing season is the crux of Vasey's business. But he also estimates early season yield potential by using a plant dissecting kit to perform a "spikelet exam" on wheat plants. The number of spikelets (developing kernels) per spike (developing wheat head) can be determined early in the season, and research indicates a good correlation between yield estimated by a spikelet exam and harvested yield.
Yield potential estimates can be made as early as the 4 to 5.5 leaf stage of the Haun growing scale. Research indicates that during this growth stage, average high temperatures above 63 degrees F will reduce the numbers of spikelets per head, which reduces yield potential. The best scenario for high spikelet numbers is early seeding with rapid emergence of a uniform stand and no hot weather during the 4 to 5.5 leaf development stage.
Vasey prefers to evaluate yield potential by performing spike/spikelet exams at the 5 to 6-leaf stage of the Haun growing scale, to estimate if high yield potential and the need for added inputs exists. He uses a dissecting kit that may be purchased for about $15 at college or univeristy bookstore that offers plant science classes. Even a razor blade or sharp pocket knife could be used, however.
He selects wheat plants from about 10 areas of a field for a representative sample, then dissects a subsample. The bigger the field, the more that should be evaluated. The spike can be found as a bulge or knob just above the joint of the wheat plant. "The further the plant grows beyond the 5.5 to 6-leaf stage, the higher that knob gets above the joint," he says.
Vasey counts spikelets or ridges on the spike to estimate yield. Each spikelet roughly represents about three bushels of yield. Thus, 15 spikelets would mean a yield potential of about 45 bushels/acre.
"Dr. Bauer in his work has found as many as 20 spikelets and as low as 10. The maximum possible under very ideal conditions would be about 23," says Vasey. He is quick to credit Armand Bauer, retired crop scientist at the USDA's Agricultural Research Service lab in Mandan, ND, for research that Vasey uses today as a basis for his crop staging and yield estimations.
The three-bushel per spikelet estimate assumes a live plant population of at least one million plants per acre, and that the main plant plus 1.6 tillers are carried into harvest. "Farmers ask '1.6 tillers?' well, that's an average; in the Red River Valley the average wheat plant develops two tillers for a total of three heads. In western North Dakota, it's closer to one main head and one tiller," says Vasey.
He says the spike/spikelet exam can also be performed on durum and winter wheat. Although there's less research to support the method on barley, Vasey says it should work, recognizing that the average barley plant will set more kernels per spike.
(For more information about early-season yield estimations, or calculating the windows for scab and midge problems, Vasey can be contacted by phone at 1-888-293-8903 or email: sprwhtdr@ndsu ext.nodak.edu) n
Remember MEY?
MEY was a buzz word about a decade ago that for some meant "maximum economic yield," and to others, "more efficient yield." Dr. Ed Vasey was an author of NDSU Extension Bulletin No. 58, "A Closer Look At the Spring Wheat Cropping System For More Efficient Yield and Sustainability." The glossy, color publication with about 100 pages was published in 1992 and contains general guidelines for intensive cereal management and more efficient economic yield. It will be mailed free by request to wheat association members in MN, ND and SD. For nonmembers, cost is $5. To order or for more information, contact the MAWG, (1-800-242-6118 or 218-253-4311) or the NDGGA (1-800-932-8822 or 701-222-2216). Refer to publication EB-58.