The following information is a Web Extra to the story "Making Your Test Plot Pay" by Darrell Smith. You can find the article in Farm Journal's 2010 Seed Guide.
For more information on hybrid numbers, and a tag illustration, see: Hybrid Corn Checkup
Move Your Plot Around
Especially if you grow continuous corn, don’t put a test plot in the same place every year, advises Farm Journal Field Agronomist Ken Ferrie.
"Entries from last year can interfere with this year’s entries," Ferrie explains. "A 14’-tall hybrid, versus a 6’ tall hybrid, planted last year, may need more nitrogen to decompose the residue. Or one of last year’s hybrids may have fallen down and begun decomposing sooner.
"Another danger is that you may plant two hybrids, in successive years, that are susceptible to the same diseases. That will lead to a yield reduction for the second hybrid, because of increased disease."