Interpreting Plot Yield Results

Yield trial results offer an opportunity to compare agricultural products in a geography similar to one’s own farm and can assist growers in selecting quality products for next season. As yield results are examined this fall and winter, keep in mind to evaluate multiple locations and scenarios, evaluate head-to-head comparisons, consider the statistical differences, and be aware of any differences that may not be related to the seed products.

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To access yield data, begin by looking online by brand or contacting your local seed representative. You may also consider looking at independent and university performance trials to see how certain seed products performed in a range of different locations and scenarios. These tests are generally conducted by maturity range with seed from a broad array of sources and tested across a variety of growing conditions within a state or region.

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Evaluate Multiple Locations. Data from a single plot location near one’s farm is only one snapshot of performance, and may not provide a complete picture of product potential. Products may yield well at one location and poorly at another. Weather, insect pressure, and fertility are just a few variables that can affect product performance across locations. Therefore, evaluating products across multiple locations allows the greatest opportunity to get an accurate picture of performance and consistency. If there is data available, an evaluation of product performance across years is also beneficial.

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The agAhead® data source is an online resource that provides harvest results and yield information for a farmer’s area. One of the features is a yield map that presents yield results from a specific zip code. Farmers can search yield results by corn and soybeans, or by location, to view local yields in an area with the interactive yield map that features individual plot results across the United States. Another feature on agAhead is the third-party reports page which provides links to independent and university performance trials. The online resource can be accessed at the following location: www.aganytime.com/Local-Yield-Results/Pages/default.aspx

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Head-to-Head Comparisons. When trying to determine if one product is superior to another, compare the products not just at one plot, but at many. Evaluate products versus the “check�? product that is used as a reference in comparing the yields of products that are in close proximity to it. The purpose of the “check�? is to provide a relative measure of product performance in that general area of the field. Evaluate products with similar traits and maturities to minimize differences due to trait protection or stress tolerance. Maturities should be within five days of each other and trait packages should be equivalent.

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Statistical differences signify that the results are unlikely to have occurred by chance and have a high probability of repeating themselves. If yields are not determined to be statistically significant, it indicates that the differences due to seed products are not large enough relative to the experimental variation in the field.

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University and independent plot results may include an LSD, which stands for least significant difference. The LSD indicates what amount of yield variation can be attributed to the product itself versus influence from outside factors. Yield differences greater than the LSD can be attributed to actual differences in genetic yield potential of products. Yield differences less than the LSD are not considered statistically different and are likely due to outside factors. Often, you will find the LSD at the bottom of the yield table in performance trial results.