By: Vince Davis and Megan Ott
Paul Esker, University of Wisconsin Extension Plant Pathologist, discussed the statistics of on-farm foliar fungicide research trials. They have developed an extensive network of on-farm trials averaging 20 to 25 research locations per year in WI over the last couple of years. They focused, with their growers, on how to emphasize appropriate statistical analysis. The foundation, of course, was Fisher’s three principles: replication, randomization, and blocking. Unfortunately, large-plot observational studies are much harder than small plot research to accomplish those principles.
There are several sources of variation from the farms – they are not the same, and treatment effects are not the same due to environmental variation. Weather data is always important, but a challenge. WI also has a wide range of soil types.
One important step for good on-farm research is to learn more about each individual field to make sure check strips are placed in an area of the field that is adequately representative of the whole field. Paul also mentioned that blocking around contours in some fields can be a major challenge. An idea of “An empirical law of heterogeneity of agricultural crops in fields” dates back to Fairfield-Smith in 1938 and even before.
The statistic that has a big financial implication to growers at the end of the day is the power to detect a difference. This is based on concepts like the p-value that represents the probability that there is, or is not, a difference related to a treatment. Very simply put, if the size of difference and the sample size are large, the power is large, but if the error variance is large, the power is low.
Paul then summarized 2007 and 2008 trials mostly using data from the treatment of Headline fungicide produced by BASF. The number one disease in Wisconsin in corn right now is anthracnose of corn. They found little differences related to crop rotation, and no differences in relation to crop maturity. They did find about a 10 bu effect due to tillage but no interaction with tillage and fungicide use. The “trend” is an advantage of 3-4 bu/acre for using Headline across all the different environments and they have not seen an increase in corn grain moistures. This fall they are looking into corn stalk ratings to better understand the influence of stalk quality.
In summary, they are finding success to using a slightly more complicated, on-farm research protocol over multiple locations. Over years, they are building ‘blocks’ over time, and their focus is on corn stalk quality in the next couple of years. Paul said an additional resource for learning more about on farm research can be found on the Plant Management Network website.
You can find Megan’s interview with Paul below:
Audio File: Paul Esker
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