Be Careful Drawing Conclusions from Test Plots

CORN ILLUSTRATED: Even strip trials need a closer look before you make decisions.

Published on: Dec 3, 2013

Test plot data has likely already arrived in your mailbox. No telling how many seed salesmen have already pulled up your drive, some you know and some you don't know. All have test plot results to hand you. If they're not in a fancy booklet, they will be soon. And all have an order book so they can sell you seed. How do you know which ones might be the right ones to do business with?

If you're going to pay attention to their test plot data, ask questions. Are they strip trials? If they're strip trials, was there a checker or test hybrid included? If so, was it every other entry, every third entry, or every fourth entry across the field?

Agronomists will question the value of checker hybrids in test plots. Their point is that replicated plots are better, where you repeat the entire test at least twice, preferably three times. From a scientific standpoint, there's no question that can help you pick out which hybrids or varieties are truly better than another more accurately. From a realistic standpoint, it's not going to happen on most farms.

Check the check: The same hybrid was planted as every third entry in this plot to get a feel for differences in soil type.
Check the check: The same hybrid was planted as every third entry in this plot to get a feel for differences in soil type.

What may happen is a strip trial. And if you can include a checker hybrid, you at least get some measure of how the hybrid you're testing does against the checker. If you run the check hybrid across the field as every third entry, for example, and it yields from 175 to 180 bushels per acre every time, then you've got a uniform plot.

However, if the yield ranges from 130 to 210 bushels per acre, then obviously soil type or some other issue caused huge differences in the check hybrid. If hybrid B next to the 210 entry yielded 215, it may not be better or even as good as hybrid B that yielded 145 bushels per acre next to the check strip that ran 118 bushels per acre.

The key is how the two hybrids did in reference to the check strip.

It's not scientific, but it will help take some bias out of your evaluation of plots. In this case it should keep you from dismissing the hybrid that made 145 bushels per acre out of hand. That's when you need to know what went on during the season, and what caused low yields on that side of the field.

The bottom line is simple: ask questions before you put too much stock in test plots.