Death comes to us all. Life's but a walking shadow | Working backwards from your 204 bu. /A figure using the Pro Farmer formula I get 57.3 ears per plot. Assuming 30 in. row widths the Pro Farmer plot is 75 sq. ft. or 0.764 ears/sq. ft. If your ear population is 33,000 per acre then your ear population is (33,000/43,560) or 0.758 ears/sq. ft. or 56.8 ears per plot and using the Pro Farmer formula you get 202.4 bu/A or a difference of 1.6 bu. not enough!
The Pro Farmer Formula assumes 60 kernels per foot or 5 kernels per inch (60/12). The ear length and count data you provide gives 4.7 (34/7.25) or 4.28 (30/7) kernels per inch. Figure the average kernel count of 4.49 kernels per inch this is 53.9 kernals per foot or 89.9 percent lower. Now your 204 bu becomes 183.4 minus the 1.6 bu from above or 181.8 bu/A. Getting closer!
Finally, the Pro Farmer formula assumes 87,120 kernels per bushel (2x43,560) while you used 90,000. This is a 3.2% difference or 6.5 bu/A (204x0.032) so 181.8 minus 6.5 is 175.3 bu./A. Pretty close!
Just out of curiosity I checked some kernel counts, a fully dry ear from last year gave 5.3 kernel per inch, an ear just beginning to dent was 5.6 kernels per inch and an ear in milk was 6 kernels per inch. Your corn has larger than expected kernels. Is it possible that your population is lower than 33,000? In the past I have observed that low population corn has much larger kernels.
This all just goes to show how uncertain the yield estimations the Pro Farmer, USDA or even the producer can be.
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Maybe this is the problem...
