Are your corn and soybean yield estimates accurate?

Are your corn and soybean yield estimates accurate?

These guidelines can help make your preharvest yield estimate more precise.

Some growers like to make storage/marketing plans for the crop prior to harvest, and a preharvest yield estimate can help them out. No doubt any estimates made in the field this year will be interesting to say the least, given the range of reports out already. The recent Pro Farmer tour shed this light on yields in western Iowa. "One group scouted 10 counties from Fremont in the southwest corner to Palo Alto in northwest Iowa," says Iowa State University Extension agronomist Clarke McGrath. "They sampled cornfields that ranged between 140.6 bushels per acre to 227.3 bushels per acre."

HARVEST BEGINS: A farmer at Prairie City in central Iowa harvested 20 acres of soybeans Tuesday of this week that averaged 71.5 bushels per acre. He had the same variety in a test plot that yielded 77 bushels per acre.

How to do your own estimates: Corn yields can be estimated after the kernel number is finalized, which is roughly two weeks after the end of pollination. For people who want an estimate of your corn crop yields, McGrath suggests you try this formula:

{(Ear #) x (# kernel rows) x (# kernels per row)}/90 = Estimated Yield in bushels per acre.

"Be sure to grab enough ears from several areas to get a representative sample," he says. Maybe grab three or four ears from five or six areas in a field. You want to sample more areas in the field if it is a large field. It is recommended to separately sample your various hybrids, tillage systems, rotations, etc.

McGrath adds: "I read once where one of the Midwest's corn researchers said this formula was accurate to around plus or minus 30 bushels per acre, so some agronomists say this is an exercise in futility, but my experiences have been pretty good with yield estimates. Like most growers, I do have to try really hard to not grab ears in the best looking parts of the field, though."

University of Illinois has an online yield estimating tool
McGrath says he tried closing his eyes and grabbing ears at random a few times, but soon decided he wasn't coordinated enough to avoid ditches, rocks, terraces, cows, etc. Anyway, while it is not always highly accurate, a lot of growers like to do yield estimates because it is often helpful to have a rough idea of yield.

The University of Illinois has an online yield estimator. It adds the dimension of kernel size. "Running this program has gotten us very close quite a few times," he notes.

Can you estimate soybean yields in the field?
Farmers say corn is hard enough to estimate the yield prior to harvest. But what about  beans? Can you estimate soybean yields in the field? McGrath says maybe you can do it with this formula that follows here. We are pretty close to being able to do this a little earlier in the growing season, he notes. But it works better at the R6 growth stage, or after), so here is the formula McGrath is familiar with: (plants per acre) x (pods per plant) x (seeds per pod) ÷ (seeds per pound) ÷ (pounds per bushel) = (bu. per acre).

However, with soybean yield estimating "I stick to what I have always said in the past," notes McGrath. "It is really tough to estimate bean yields by counting pods, plants, etc. When I have counted pods and plants and all of that, the yield calculations usually don't come as close as when the farmer and I take a quick look at the field and make a visual guess. So, unless you really want to do a lot of soybean math, go golfing, fishing, catch a high school football game, whatever else you want to do instead of counting pods and plants and seeds. Maybe you have a method you like for estimating bean yields; if so, please share it with us."

TAGS: USDA Extension
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