Ohio’s corn and soybean crops experienced exceptional growing conditions in 2015, including record rainfall in June and July followed by a drier than normal August conditions in many areas. The persistent rains saturated soils and caused localized ponding and flooding. These conditions resulted in root damage and N loss that led to uneven crop growth and development between and within fields. Agronomists often question the value of test plot data when adverse growing conditions severely limit yield potential.
The validity of test plot results depends primarily on whether effects of the varied stress conditions are uniform across test plots. If not, test plot data may be questionable. To be certain that effects of stress were fairly uniform, it would be necessary to monitor test plots on a regular basis to determine crop response to the various stresses as they occurred; however, such monitoring was probably unlikely in many test plot fields.
Another problem with test plot results is that the various yield limiting factors may accentuate the natural “variability” already existing in the field, and may thereby further “mask” the true treatment effects that are being compared. Stress conditions like the ponding and saturated soils this year coupled with slight differences in soil organic matter, drainage, weed control, etc. across a field may magnify differences in crop performance.
If one assumes that the varied stress conditions affected test plots uniformly within a field, then interpretation of test plot data becomes an issue. This issue can be especially relevant when evaluating results of hybrid and cultivar performance trials affected by excessive soil moisture. Did a hybrid or cultivar yield well under saturated soils because it genuinely possessed some flooding tolerance or because it was planted in better drained areas of the field? This year we have more than a 100 bushels per acre difference in plot yield between hybrid entries planted at different locations within a field that are related to soil drainage and N loss. Usually there are striking visual differences between such plots associated with plant height and overall plant health but differences are not always pronounced.
Test plot information this year can still be very useful but take precautions. Results from single on-farm strip tests should not be used to make a decision on adoption of a treatment or variety. Even replicated data from a single test site should be avoided, especially if the site was characterized by abnormal growing conditions. Use test plot data from multiple sites (and preferably from at least two years of testing) and inquire about the weather patterns and conditions associated with the results. Look for consistency in a product or cultivar’s performance across a range of environmental conditions.