AMES, Iowa - With spring’s arrival, it is time to plant oats, spring wheat and barley. Farmers typically plant two to three bushels of small grains per acre, but there is a better way to ensure plant populations to optimize small grain yields.
New research from Iowa State University shows that farmers should use the same level of management for small grains as they do when managing corn or soybeans. By using seed counts per acre when planting, instead of a “by the bushel” rate calculation, farmers can receive both yield and financial benefits.
For maximum oat yields, harvest plant populations should be 1.0 to 1.3 million plants per acre, or approximately 22 to 29 plants per square foot, according to recent research by Mary Wiedenhoeft, professor of agronomy at Iowa State University, and David Weisberger, graduate student in agronomy. The study is supported by the Iowa Organic Association.
Several factors affect the final plant stand at oat harvest: The desired final plant stand, number of oat seeds per pound, germination rate in the seed lot and expected stand loss from irregular seeding depth or early plant death.
“Calculating seeding rates in terms of seeds per acre rather than bushels will improve planting accuracy and help optimize yields,” said Weisberger. “Oat bushels are standardized at 32 pounds per bushel but there is a range of actual test weights that affect the accuracy of planting by the bushel. Additionally, seed quantities vary from 12,000 to 17,000 seeds per pound depending on the oat cultivar and growing conditions under which the seed was produced.”
Small grain seed counts per pound are not commonly listed on seed bags, but farmers can request that information seed dealers can provide that information if they have an automated seed counter. If not, farmers can determine seed counts themselves by weighing an ounce of seed on a digital scale, counting the seeds per ounce, and multiplying that by 16 to calculate seeds per pound.
When calculating the seed drop rate, it is important to account for the germination rate of the seed lot, typically 92-95 percent, and for typical stand establishment losses of 10-20 percent due to early irregular seeding depths and early season plant mortality. This will increase the amount of seed needed at planting. A recommended formula for calculating oat seeding rate is:
- Determine desired final stand per acre and divide by: (1-expected stand establishment loss).
- Calculate seeds per pound and multiply by the germination rate of the seed lot.
- Divide 1 by 2 for the final seeding rate.
The Department of Agriculture in Alberta, Canada, has developed an online calculator to determine seeding rates for oats and other small grains. Note that the rates in Canada are calculated using grams, not ounces. This can be converted by using 28.35 grams per ounce.
If oat or other small grain planting is delayed, fewer tillers (plant stems that produce seed heads from an individual seedling) will form and reduced grain yields will result. The University of Minnesota advises increasing seeding rates by 1 percent for each day after the optimum spring small grain seeding date to compensate for less tillering.
Research is ongoing at Iowa State University to determine the optimum oat seeding rates for different seeding dates in Iowa.
Small grains acres are increasing on organic farms and by farmers growing cover crop seed, according to Margaret Smith, a specialist with the ISU Extension and Outreach Value Added Agriculture program. Small grain growers can benefit by increasing management practices for these crops.
Mary Wiedenhoeft, Professor of Agronomy, 515-294-3274, firstname.lastname@example.org
David Weisberger, Graduate Student in Agronomy, 515-294-2230, email@example.com