Field research trials are an important part of understanding how specific agronomic practices can improve farm productivity. Universities such as Purdue use both research station and on-farm research trials conducted across their state to help drive recommendations and provide management information for farmers.
However, some of our research practices and conclusions may differ from various private-sector research trials and potentially what you may see on your own farm. For example, questions may arrive as to:
- “Why did they set up the research trial that way?”
- “What are those letters next to the yield values they are presenting?”
- “Why does it seem the university never sees any yield responses from various products?”
Therefore, it is important to understand how we approach field research trials, the steps we take to determine our conclusions, and how understanding these approaches can help you better understand and test practices more accurately on your own farm.
Ask Critical Questions
The first questions I often ask people when discussing research results are:
- Do you have a yield monitor in your combine?
- When traveling across the field during harvest, do those yield values stay the same?
The answer I receive 100% of the time is no (if the answer is yes, you may need to consider a new monitor), and this is largely due to the variability throughout the field caused by soil type differences, elevation differences, etc.
When setting up field research trials we often designate a treatment (such as with a new product) and compare that to a non-treated, business-as-usual control. And one of the most important questions we ask after harvest is was the yield difference observed truly caused by the product we applied, or was the yield difference only due to the treated areas being in a more productive part of the field?
For example, in Figure 1, if I split a field in half and apply my treatment on one half of the field and don’t apply my treatment on the other half of the field, I may find a yield difference of 15 bushels per acre and think maybe I should apply this product on all of my acres.
However, when you look closer, it is easy to see that the treated area of the field encompassed a larger portion of one soil type, whereas the non-treated area encompassed a larger portion of another soil type. Therefore, it is difficult to differentiate if the yield response was due to the product applied or was it due to the treated area being located in a more productive area of the field.
Figure 1. Example of a split-field comparison between a non-treated control and a designated treatment.
In our university research trials, we approach testing a treatment within a field using randomization, replication (repetition of an experiment in similar conditions) and statistics (as shown in Figure 2 and Table 1). For example, if you compare data in Figure 1 and Figure 2, Figure 2 highlights how we typically set up one of our research trials using replication and randomization of the treated and non-treated passes to account for field differences. Each of these practices help us improve the reliability of our conclusions, account for random error (such as field variability) and determine the true causes of yield differences observed.
Multiple Years, Multiple Locations
Furthermore, it is also important for us to perform these research trials across multiple locations and multiple years to determine how treatment responses may differ in different fields and different environments. We also use statistical models to help determine our conclusions (Table 1). Using statistics helps us determine if the differences we detect are due to random error or due to the treatment we tested.
For example, if you have ever seen university data presented (such as the data presented in this report), you have probably seen data presented similar to Table 1. At first glance, after we randomized and replicated our treatments (Figure 2), the treated areas seem to have increased corn yield by 4 bushels per acre as shown in Table 1. However, our conclusions suggested no yield differences were observed.
Through the research steps we implemented, it was determined that the yield difference was due to random error (such as field variability) and not due to the product or management practice that was tested. The letters next to the yield values help us highlight where statistical (yield differences due to treatments) differences were observed.
Figure 2. Example of a replicated and randomized field research trial comparison between a non-treated control and a designated treatment.
Corn Yield Per Acre
*Average yield values which contain the same corresponding letters are not statistically different (P>0.1) from each other.
Table 1. Corn grain yield comparisons between the non-treated control and an imposed treatment following a randomized and replicated field research trial.
When testing a new product or practice on your own farm, it is important to think about how to design and set up a trial to accurately test the new product or practice. Just because a yield difference is observed, doesn’t always mean the new product or practice you tested is the reason for this difference.
At Purdue, it is our goal to accurately assess new products and practices to determine whether or not these are truly the reason behind observed yield differences. In addition, as you sit in on various meetings, presentations and examine research results, ask yourself, "How did they design and set up this research trial? Did they use randomization, replication and statistics? If not, are the yield differences being discussed truly due to the product applied?"
Also ask how many different environments and over how many years this product was tested. Understanding and asking these questions can help determine the best products and management practices to implement and improve your operation.