Blogging by the Bushel
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CORN ILLUSTRATED: Dryer shrinkage takes out bushels. Make sure you’re talking 15.5% corn on bushels per acre.

Tom Bechman

Published: Sep 17, 2013

If you want to win bragging rights at the coffee shop, weigh your 28% corn you harvest in the next few days or weeks and divide by 56. You’ll get a much bigger number than if you dry the corn first, then weigh it. Always make sure that when someone begins talking yields, especially if it’s a seed salesman trying to show you how well his hybrids performed in a plot, that he’s talking dry bushels.

The Purdue University Corn & Soybean Field Guide, now available as an app for the iPad, explains how shrinkage works. As moisture is removed, weight is removed. It’s a simple concept, and most people honor reporting as dry bushels, but it doesn’t hurt to be sure.

How much dry corn? The yield monitor takes the guess work out if it’s calibrated right. Without a yield monitor, you may not have as much corn per acre as you think while combining if you’re just guessing by volume on wet corn.

Here’s an example. Suppose you have 56,000 pounds of grain on a semi at 26% moisture. You typically can carry 1,000 bushels of corn out of the bin in the semi, so you assume you’ve got a pretty good thing going on yield in that field. So what if moisture knocks off a little bit.

It’s more than ‘a little bit.’

Divide 56,000 by 56 and you’ve got 1,000 wet bushels. However, when you dry to 15%, you must include a shrink factor. Grain specialists have worked out the formulas that tell you what factor to use to know how much weight of corn you will have left after you dry it to 15%.

In this case, multiply the wet weight by 0.01176. You get 129.6 bushels. That’s how much of that load was water, not real corn. Subtract that from the original weight, then divide by 56. You’ve got 870.6 bushels left. That’s a pretty hefty drop. Figure field yields using 870 bushels, say off 5 acres, instead of 1,000 bushels. Your wet yield was 200 bushel per acre. The dry yield is 174 bushels per acre.

That’s why elevators either dock you, factor in shrinkage, or some combination of both when you deliver grain. And that was at 26% moisture. If you start shelling this week, some of you will be harvesting at higher moisture content.

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