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You Can’t Compare Yield By Looking

You and your neighbour have wheat crops side by side, seeded around the same day. They are the same variety. You know your neighbour sprayed insecticide and you didn’t. He also applied a preseed burnoff that you didn’t. Yet, in the end, the two crops looked like they yielded about the same. So did the neighbour waste his money on these extra treatments?

That’s really hard to say because visual assessment is often a poor predictor of yield. Yields you think are “about the same” might be five to 10 bushels per acre different — or more — which may be enough to justify those extra treatments.

Garry Ropchan is the research co-ordinator with the Central Peace Conservation Society in Grimshaw, Alta. On his plot tours, he tests farmers’ ability to guess yields. Being in the ballpark is very difficult, even for experienced farmers.

For his yield-guessing contest, Garry gives each farmer a sheet with all the plots on it, the treatments and so forth and asks them to guess what the net yield, dry yield, and zero per cent dockage yields will be for each plot. To spur their competitive spirits, Garry gives $100 to whoever was closest to the overall average after harvest. “Suddenly these producers started going up and down the plots, standing at borders and looking left and right, counting kernels and pods and best of all, they were shielding their pages from their neighbours!,” Garry says.

So how did they do? “In most cases, even with the best producers that I’ve worked with, they can accurately estimate yields 15 to 20 per cent of the time. And for evaluating different agronomic practices, that just doesn’t cut it,” Garry says. “The other funny thing is that a given producer is not consistently under or over, but sometimes over and sometimes under. So it is not a case of them looking at things the same way, above or below true yield each time, but one plot they”ll guess higher, and one plot lower.”

Garry’s contest was an effort to get the producers to look more closely at the plots and to have a bit of fun while doing it. But it also demonstrates that visual assessment is no substitute for scientific trials using weigh wagons and eliminating all variables when comparing yield results.

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