Source: Iowa Soybean Association news release
One of the most important management decisions farmers make is selecting the best soybean varieties for their soils and farming conditions.
To illustrate this, consider results from an Iowa Soybean Association (ISA) on-farm trial where two seed varieties were split-planted across the field. The varieties were termed “offensive” and “defensive” by their seed company. The offensive variety was characterized by being high-yielding in good soils with little disease and stress tolerance. The defensive variety was characterized as lower yielding, but more tolerant of diseases and moisture stress.
In the ISA trial, the field was divided into high, medium and low yielding management zones according to yield history. These management zones were overlaid upon the yield data to understand if varieties performed differently in each zone.
Figure 1 shows the offensive variety was higher yielding in the highest yield zone of the field, while the defensive variety yielded three bushels more than the offensive variety in the less productive zones.
This data illustrates the importance of variety selection on a field-by-field basis as well as within a field.
Figure 1. Results from a soybean split-planter trial.
Selecting seed varieties
To select the best varieties for your operation, you must look at many yield trial results from various sources. As much as possible, find trial data for soils and yield environments that are like the ones you farm. For example, if the average yield of the trial is 70 bushels, but you have a field that struggles to raise 50 bushels, the top variety in this trial may not be the best variety for your farms.
It is understandable to view seed company trial results with skepticism, but keep in mind some of this data can be very good. Typically, seed companies have rich on-farm data from multiple locations with varieties from their own lineup. The seed company has no vested interest in which variety you choose from their selection of products, so this data can be trusted when finding varieties that are best adapted for your farming conditions and soils.
Where seed company trials falter is when they compare varieties against competing seed companies. Typically, these trials compare multiple varieties of one seed company versus a few competitors. This stacks the odds in favor of the seed company as they have more chances to win by chance alone.
More sources to help with selection
Other sources of yield information include university and independent testing services. These trials can provide valuable information especially on traits like lodging and seed shattering. However, these trials are typically small plot studies and not all companies participate in this kind of testing.
Many farmers routinely test new varieties on their own farms. This can provide very useful information, but some caution is warranted. The yield results from a single year of testing are valuable and indicative for that year’s weather patterns. When you compare your own data with data from other locations with similar soils, you have greater predictive power of how that variety will respond to future weather patterns and field conditions. It is difficult to get good comparisons of varieties across seed brands. Shared testing of new varieties with neighboring farmers is a very good practice to optimize seed selection.
There is no substitute for knowing your fields when it comes to variety selection. For example, fields with a history of white mold should be planted to varieties with greater white mold tolerance. In poorly drained fields, look for sources of resistance to phytophthora and sudden death syndrome.
While this has never been proven scientifically, it makes sense to select varieties based upon your seeding rate and row spacing. Consider a variety with a narrow canopy trait planted in 30″ rows. This could lead to a more open canopy resulting in wasted sunlight or less suppression of weeds. It makes intuitive sense to plant narrow-canopy soybeans in narrow row spacing and wider canopy types in wider rows. Similarly, if your seeding rates are ultra-low, you will want varieties that tend to branch more or are wider in canopy.
It is estimated that soybean yields increase by about one-third of a bushel per acre per year due to genetic improvement. While some new varieties show this response, other new varieties may not yield better than those currently used. Therefore, seed selection in soybean production has a large impact on profitability.
Scott Nelson can be reached at firstname.lastname@example.org