USDA has revealed the cause of the data error in its September corn estimates, acknowledging that incorrect acreage weights were used to combine irrigated and nonirrigated field observations. The error affected September plant populations, ear counts and yield forecasts for Kansas and Nebraska, the 10-state regional averages and national figures.
In a statement issued Saturday, Oct. 24, USDA’s National Agricultural Statistics Service (NASS) provided details on the miscalculation following a review of its September and October estimation procedures. The explanation came one day after the agency acknowledged a data processing error had affected its September report, but initially provided no details on what had caused it.
Despite revising the September baseline, NASS said its October corn yield and production forecasts remained unchanged. The October estimate, released Oct. 9, put the national corn yield at 181.2 bu. per acre, up 2.7 bu. from September’s original estimate of 178.5 bu. per acre. Production remained projected at more than 16 billion bushels.
What Changed in USDA’s September Corn Estimates?
NASS issued the following corrected September yield estimates:
- Kansas: 119 bu. per acre, down 3 bu. from the original estimate.
- Nebraska: 182 bu. per acre, up 5 bu. from the original estimate.
- United States: 178.8 bu. per acre, up 0.3 bu. from the original estimate.
The agency said it updated all affected tables, charts and narrative sections across its Crop Production reports to reflect the corrections.
Why Nebraska’s Corn Yield Jump Drew Scrutiny
The revisions offer crucial context for the market backlash that followed the Oct. 9 report, when USDA increased the national yield estimate by nearly 3 bu. per acre and sent corn futures sharply lower.
Nebraska was at the center of the controversy after USDA raised its October corn yield estimate to 188 bu. per acre — an 11-bu. month-over-month increase based on September’s original 177-bu. figure. Analysts questioned the jump after examining field data, which suggested that roughly 90% of Nebraska fields sampled in September were nonirrigated versus only 10% irrigated. By October, the sampling balance returned to a normal distribution of roughly 55% irrigated and 45% nonirrigated.
By applying the corrected acreage weights, NASS raised Nebraska’s September yield to 182 bu. per acre, effectively cutting the month-over-month yield leap from 11 bu. to 6 bu.
Lingering Industry Questions
While NASS said the issue was confined to a calculation mistake, Chip Flory, Farm Journal economist and host of AgriTalk AM, still has questions about the data behind the estimates.
“The fact that USDA now says, ‘The review identified a September processing error involving incorrect acreage weights used to combine irrigated and non-irrigated objective yield observations for Kansas and Nebraska,’ certainly makes this look like an accounting error and nothing more,” Flory said. “However, as I have asked questions at different levels of this process, there are questions that remain unanswered about the data-gathering from the objective yield plots in September.”
What Happens Next? USDA Weighs In
In its Saturday statement, NASS thanked the farmers and data users who raised concerns about the estimates.
“Moving forward, we will implement additional pre-publication checks to verify acreage weights and validate objective yield calculations,” the agency said. “We are evaluating further improvements to strengthen our quality-control procedures.”
NASS also reiterated its commitment to providing timely, accurate and reliable ag statistics and to promptly communicating and correcting errors identified in published data.
