Corn harvested in the Corn Watch ’19 field will be wet. It’s a function of planting May 28 with mid- to full-season hybrids. Dave Nanda expects respectable yields and relatively high-moisture content.
“One hybrid didn’t reach black layer until the end of September, and the other was even later,” Nanda says. He’s director of genetics for Seed Genetics-Direct, Jeffersonville, Ohio. Seed Genetics-Direct sponsors Corn Watch ’19.
That’s why you must convert wet weights to dry bushels before determining yield, he says. Most yield monitors do this, but the results are only meaningful if the monitor is calibrated properly. When conditions change, such as if moisture content varies significantly between fields, recalibrate, experts recommend.
Bob Nielsen, Purdue University Extension corn specialist, outlines converting to dry bushels in his article Converting Wet Corn Weight to Dry Corn Weight.
He explains how to correct for weight of water removed during drying. He doesn’t address anticipated weight loss from dry matter loss during drying and handling, sometimes called invisible shrink. Weight loss due to removing water to 15% moisture is the greatest factor, Nielsen says.
First, convert wet weight, above 15% moisture, to absolute dry weight, at 0% moisture. Then convert absolute dry weight back to a standard dry weight at 15% moisture. Follow these steps:
- If initial grain moisture is 20%, initial dry matter content is 80% (100 minus 20).
- If desired final moisture content is 15%, ending dry matter content is 85% (100 minus 15).
- Multiply weight of wet grain by initial percent of dry matter; then divide by desired ending percent dry matter.
Suppose you have 100,000 pounds of grain at 20% moisture. That’s 80,000 pounds of absolute dry matter (100,000 times 0.80). Correcting back to 15% standard moisture, that’s 94,118 pounds at 15% (80,000 divided by 0.85). To get bushels, divide by 56: 94,118 pounds divided by 56 equals 1,681 bushels at 15% moisture.
If you just divide the original wet weight — 100,000 pounds — by 56, you would think you had 1,786 bushels.
Here’s an example from a trial, not in the Corn Watch ’19 field. You dump a pass into a grain cart with scales. The weight is 3,500 pounds. The yield monitor says you harvested 0.28 acre. The grain moisture tester reads 25% corn.
Convert initial weight to absolute dry matter. At 25% corn, initial dry matter is 75%. You have 2,625 pounds at 0% moisture (3,500 times 0.75). At 15% final moisture, that’s 3,088 pounds (2,625 divided by 0.85).
So, you have 55.1 bushels (3,088 divided by 56) from 0.28 acre of 15% corn. To get bushels per acre, divide by acreage (55.1 divided by 0.28) to get 196.8 bushels per acre.
If you used the wet weight of 3,500 pounds, you would arrive at 223 bushels per acre. That makes for coffee shop bragging rights but doesn’t help with management decisions.