Spring wheat is seeded at higher population compared to winter wheat. Since wheat seed varies in seed size (seeds/lb) and germination rates, the following equation can be used to determine seeding rate in pounds per acre.
Seeding Rate (lbs/acre) = ((desired stand in plants per acre)/(1-expected stand loss))/((seeds per pound)X(% germinaton))
The expected stand loss can vary between 10 and 20 percent, depending on seedbed conditions. Germination should be found on the seed tag. If planting is delayed past the optimum time period, the initial stand should be increased by 1 percent for each day planting is delayed. In general, an initial stand of 30 to 32 plants/ft2, which is about 1.3 to 1.4 million plants/acre, maximizes yield potential.
Yield components of wheat:
- heads per live seed planted,
- heads per aquare foot,
- seeds per head,
- seed size
can be flexed to reach the same yield with fewer plants. Heads per plant, or tillering, is a trait affected by environmental conditions, including soil fertility, planting date, and agronomic practices such as seeding rate. The number of heads per pure live seed planted decreases, with increased seeding rates. Conversely, a decreased seeding rate results in a decreased number of seeds per head and larger seeds.
Data from 2013 to 2015 including 12 hard red spring wheat products planted across Minnesota and North Dakota demonstrates tillering can be predictive. In general, southern locations had more stems per plant, and wheat planted in high-yielding locations had fewer stems per plant. A general goal is to manage fields so each plant produces three tillers.
Scouting for tillers should begin when main stems have three full leaves. Quantifying tillers is important for management practices. Tillering can be manipulated with nitrogen applications. Weed management also depends on tiller scouting as some labels require tillers to have two to three leaves before herbicide application.
Seeding rates can be reduced for products that tiller well and are planted timely in good soil conditions. It may be beneficial to increase seeding rates for products that tiller less, are planted later than the optimum, or are planted in rough seedbed conditions.
Height of Wheat Plants
The heights of wheat products can vary from short and medium-short to tall. Environmental conditions, including weather and soil fertility, affect stress on stems and vegetative growth. Tall wheat products, fields with high yield potential, and over seeding can lead to plants susceptible to lodging. Lodging increases chances for disease, complicates harvest, and negatively affects yield potential. In the range of acceptable seeding rates, shorter wheat products with strong straw can be planted at higher seeding rates with less risk of lodging.
Seed Size of Wheat Products
Wheat has traditionally been planted by the pound. However, variations in seed size and density can lead to great differences in the number of seeds being planted from that pound of seed. Larger, denser seeds means fewer seeds planted. This can affect weed growth, delay maturity, and create an over-reliance on tillering. Smaller, lighter seeds can cause over seeding and could lead to lodging, increased disease, and greater input costs. Seeding rates are more accurate and the likelihood of achieving the targeted plant stand is improved when the rate is calculated based on the seeds per pound for the specific seed lot being planted. Ask your wheat seed dealer about seed counts for the wheat product you purchase. WestBred seed suppliers running the ConnectIN Wheat Insight System can offer seed counts for each product along with Optimal Seeding Rate recommendations.
In addition to these agronomic reasons, calculating optimal seeding rates is important to farmers for economic reasons. WestBred seed suppliers have access to new tools to determine seeding rate based on wheat seed product, seed size and density, geography, planting date, and production practices. Discuss these factors with your WestBred brand representative to get greater insight on what needs to be purchased and planted in each field. Seeding rates tailored to wheat products can help farmers maximize the return on their seed investment while helping mitigate risks associated with under or over seeding.
Evaluating seed product yield test data from two or more years and multiple locations can provide a more accurate indication of the potential performance of each wheat product. Purchasing certified seed can help ensure the wheat product is free of weed seed and certain diseases and offers the desired germination percentage. Consult your seed brand representative for more information on products best-adapted to your geography and the specific agronomic needs of your farm.