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Picking next year's seed? Watch this variable

Though there's growing speculation that this year's drought will stretch into the 2013 crop year, it's fueling a lot of uncertainty about what corn and soybean varieties might perform best next year. It's an especially precarious decision to make right now, with yield and other performance data being as sketchy as it is in some areas because of the drought's overwhelming influence.

But, when you're making a concrete decision like this one, you have to use whatever data is at your disposal, and that data holds a few pointers for buying seed for next year, one agronomy expert says. If you know where to look.

"Though some may have a hunch that conditions will be unusually dry again next year, looking at yields over the years suggests that unusual growing seasons don’t repeat themselves very often," says University of Illinois Extension agronomist Emerson Nafziger. "So our best guess is that conditions next year will be 'average,' meaning that it makes sense to use data from trials where conditions were more or less 'average' this year."

Nafziger leads University of Illinois Extension's corn variety trials each year. This year's been a rough one for gleaning a lot of yield data from field variety trials, but one variable can be of big value when you're filing through data from either universities or seed companies, both of which are key elements in making a good variety selection decision. The coefficient of variation (CV) is a measure of how a variety performed across different sites, something that can essentially show how adaptable that variety is among different climes.

"The CV, which is a percentage, is a kind of quality measure for the trial. In the case of regional averages, the CV is a good indicator of how consistent performance was across locations in the region," Nafziger says. "Values of CV within well-run trials tend to be in the range of 5% to 10%. Higher-average yields tend to lower the CV. And both low yields and non-uniform conditions tend to raise the CV. Values above 15% or 20% for yield often indicate that the trial had problems and that the data may not be very trustworthy -- that is, some entries probably "got lucky" by being in better places in the field while others suffered the opposite. Such trials often would not produce similar results if run again under better conditions, so they are not considered to be very predictive of future performance."

Though the CV is typically higher over time across multiple test plot locations versus a single spot, that's not a bad thing, because it usually is a better predictor of performance across a wider variety of growing conditions even if the CV spread is higher than in a single field test.

So, how can you be sure you're making a good hybrid selection decision based on this year's data? In short, do your homework.

"Understand that most varieties are backed by a large body of data, from trials run over many sites and several years by the originating seed company. Testing is widespread before release, while university trials typically include entries only after release. Most of the data on performance are held by companies, and company personnel use them, along with some university trial data, to decide what seed to produce and what to sell," Nafziger says. "So while university trials are important as a means to compare entries from many different sources and companies, they are not, and should not be, the only or even the major place to look at performance data. For that, find companies you trust that sell hybrids and varieties that you know do well, and use university trials mostly as a way to backstop your decisions on what varieties you choose to use."

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