Now is the time to see how this year’s crop turned out. What will you find when you inspect cornfields?
You need to count plants per 1/1,000 acre, and then determine average number of rows of kernels and average number of kernels per row. According to the Purdue Corn and Soybean Field Guide, the formula is ears per acre times (kernel rows times kernels per row) divided by fudge factor, which is based on kernels per bushel.
“The fudge factor is the big unknown,” says Dan Quinn, Purdue Extension corn specialist. “Number of kernels per bushel varies by hybrid and year to year, depending upon weather conditions.”
Indeed, Mark Jeschke, agronomy manager for Pioneer, Johnston, Iowa, says traditionally, most agronomists used 90,000 as the fudge factor. However, for most modern hybrids, a lower number is more representative.
“We have found that 80,000 is often a better choice,” Jeschke says. “In some cases, it may be closer to 70,000. And in very good years, it can even be lower. That’s because kernel weight impacts it, and years with good grain fill conditions produce higher weight kernels.”
Yield estimate examples
See how much variation in kernel weight impacts yield estimates. Ears per acre, number of rows around the ear and kernels per row will remain constant. Only number of kernels per bushel will change, reflecting changes in kernel weight.
In each case, assume 32 ears per acre with 16 rows around and 40 kernels per row.
Example 1. Start with what Jeschke considers an average fudge factor today: 80,000 kernels per bushel, so the equation uses 80. The math is: 32 × (16 × 40) = 20,480 ÷ 80 = 256 bushels per acre.
Example 2. This hybrid is noted for having large kernels with high kernel weight. Use 72 as the fudge factor. The math is: 32 × (16 × 40) = 20,480 ÷ 72 = 284 bushels per acre.
Example 3. It was a very good year, especially during grain fill. You planted the hybrid that averages 72 as a fudge factor. However, this time, due to deeper kernels and larger kernel weight, it averages 66,000 kernels per bushel, with a fudge factor of 66. The math is: 20,480 divided by 66 = 310 bushels per acre.
Example 4. Your cousin didn’t get favorable weather. Kernels are smaller, so his average count for kernels per bushel is 85,000. The math is: 20,480 ÷ 85 = 241 bushels per acre.
Example 5. One of your cousin’s hybrids has smaller kernel size, and the weather didn’t help this year. Fudge factor is 95. The math is: 20,480 divided by 95 = 215 bushels per acre.
Summary
Take another look at the examples. Recall that in the field, you counted the same populations, equal to 32,000 plants per acre, assuming each produced one ear. Ears averaged 16 rows and 40 kernels per row.
Yet due to hybrid differences and weather conditions, there is a wide swing in possible yield, from 215 to 310 bushels per acre — a 95-bushel-per-acre spread.
“It really makes the point that kernel size and kernel weight matter,” Quinn emphasizes. “What happens during grain fill is critical.”