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Corn+Soybean Digest

How to Interpret Yield Trial Results

Selecting the appropriate mix of corn hybrids or soybean varieties is essential for maximizing yield potential. It follows, then, that having a sound strategy for evaluating potential choices and making timely decisions can improve profitability.

Yield trial data are available from many sources. Most are useful in comparing relative performance for the current growing season, but few of those resources can be helpful in making variety selection decisions for your operation. Knowing the differences can impact your bottom line.

Show plots, demonstrations and even single-location replicated yield trials have almost no value for estimating variety performance for the next season. Multi-location and multi-year data are always more predictive sources of information when making variety selections. Look for trials that use randomization, replication and multiple locations within a region.

All data should include some measure of experimental variability, such as a least significant difference or a coefficient of variation. Transparency in testing methodology and analysis procedures helps ensure impartial data. If some of this information is unavailable, ask why. Any tests that meet these criteria will be advantageous in variety selection.

More entries in a test mean more potential winners for your farm. In 2007, the Iowa Crop Performance Tests evaluated over 700 corn hybrids and soybean varieties in more than 30,000 yield trial plots all around Iowa.

Growers should begin with a clear understanding of the qualities preferred or needed in the crop. Soybeans may need resistance to SCN, SDS, brown stem rot, Phytophthora, white mold, etc. Some growers may prefer an insect or herbicide trait in their corn hybrids. Insecticidal seed treatments are available for either crop, but are they beneficial on your farm?

After this, focus on varieties that match your desired maturity range(s). Using these criteria can quickly pare down an extensive list of candidates. Then yield and gross value comparisons can be done to make final selections.

For more information, see

Jim Rouse is program manager of the Iowa Crop Improvement Association's corn and soybean tests at Iowa State University.

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