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What Do the Results from Recent Seeding Rate Studies Suggest for New Spring Wheat Varieties?

Last season we concluded a rather large multi-year, multi-location experiment to determine the optimum seeding rate for a range of diverse spring wheat varieties. Because of the large number of new spring wheat varieties made available to growers in recent years, we often get questions about how heavy a new variety should be seeded. In most cases we simple do not have data to support a variety-specific recommendation. Furthermore, generating this information can be expensive and since the environment can play a critical role in the outcome of this type of research, testing must be done in multiple environments and seasons to ensure that the results will be relevant to the varied environments in which the new variety is to be grown. In the study we just concluded we tried to elucidate principles that could be used to guide the decision as to how much to seed of a new varieties using its known genetic and agronomic characteristics and information about the environment in which it will be grown.

The following are a few of the findings and principles that we have learned:
  1. Averaged across all environments and varieties, the highest yield was obtained at the 1.40 million seeds per acre seeding rate. The optimum derived seeding rate based on the regression equations developed from this research was 1.47 million seeds per acre.
  2. Varieties differed in their response to seeding rate. The optimum seeding rate to varied from 600,000 seeds per acre for Sabin to 2.0 million seeds for Kuntz. This substantial difference strongly suggests the importance of a variety-specific seeding rate recommendation. Fortunately, variety characteristics were found to provide guidance as to what that optimum might be in the absence of empirical data.
  3. Lodging increased as seeding rate increased. This is a well-established relationship. Nevertheless, this result gives emphasis to the importance of being conservative on seeding rates when growing a variety with a known propensity to lodging. The optimum seeding rate for Briggs, a variety with weak straw, was 1.02 million seeds per acre, while the optimum seeding rate for Rollag, one of the most lodging resistant varieties in the study, was 1.84 million seeds per acre.
  4. A variety that tillers well, requires a lower seeding rate than one that does not. As an example, Albany which tillers profusely at low seeding rates had an optimum seeding rate across all environments of 1.06 million seeds per acre, while Kuntz, the variety that produced the lowest number of tillers at a given seeding rate in our study, had an optimum of 2.03 million seeds per acre.
  5. Environment plays a significant the determination of the optimum seeding rate. The optimum seeding rate for the bottom seven yielding environments in our study was 1.66 million seeds per acre, while in the top seven yielding environments the optimum seeding rate as 1.33 million seeds per acre. These finding suggests that in higher yielding environments (i.e. >65 bu per acre), seeding rates need not be increased to achieve higher yields, but in fact should probably be reduced slightly. Conversely, for lower yielding environments, there may be an economical advantage to increasing the seeding rate over the general recommendation of 1.4 million seeds per acre. Furthermore, this supports the recommendation of using a slightly higher seeding rate when planting is delayed beyond the optimum window.

The optimum seeding rates discussed above are for yield and not economic returns. We have not yet incorporate the price of seed and the value of the grain produced into our analysis. Nevertheless, we can safely state that in higher yielding environments when planting a variety that tillers well and that has reasonable straw strength, using seeding rates greater than about 1.4 million seeds per acre will not return extra value to your operation. Seeding shorter statured varieties like Rollag and Linkert, on the other hand, at seeding rates higher than 1.4 million seeds per acre will probably result in a positive economic return, especially for environments that are low to moderate for yield.

Submitted by Joel Ransom, Extension Agronomist for Cereal Crops,, Grant Mehring, Research Specialist and Jochum Wiersma, Extension Agronomist, University of Minnesota

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