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Corn Harvest Quality Report 2012/2013

Contents

  1. Harvest Quality Highlights
  2. Introduction
  3. Quality Test Results
  4. Moisture
  5. Chemical Composition
  6. Physical Factors
  7. Mycotoxins
  8. Crop and Weather Conditions
  9. Planting and Early Growth Conditions - Spring (March-May)
  10. Pollination and Grain Fill Conditions - Summer (June-August)
  11. Harvest Conditions (August-October +)
  12. U.S. Corn Production, Usage, Outlook
  13. U.S. Corn Use and Ending Stocks
  14. Outlook
  15. Survey and Statistical Analysis Methods
  16. Survey Design and Sampling
  17. Statistical Analysis
  18. Testing Analysis Methods
  19. Corn Grading Factors
  20. Moisture
  21. Chemical Composition
  22. Physical Factors
  23. Mycotoxin Testing
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VI. SURVEY AND STATISTICAL ANALYSIS METHODS

A. Overview

The key points for the survey design and sampling and statistical analysis for this Harvest Report 2012/13 are as follows:

  • Following the methodology developed for the Harvest Report 2011/12, the Council proportionately stratified the samples according to Agricultural Statistical Districts (ASDs) across 12 key corn producing states representing 99% of U.S. corn exports.
  • A total of 559 samples collected from the 12 states was targeted to achieve a maximum ±10% relative margin of error (Relative ME) at the 95% confidence level.
  • A total of 637 unblended corn samples pulled from inbound farm-originated trucks was received from local elevators from September 6 through November 26, 2012, and tested.
  • A proportionate stratified sampling technique was used for the mycotoxin testing across the ASDs in the 12 states surveyed for the other quality factors. This sampling resulted in 177 samples being tested for aflatoxins and DON.
  • Weighted averages and standard deviations following standard statistical techniques for proportionate stratified sampling were calculated for the U.S. Aggregate and the three Export Catchment Areas (ECAs).
  • To evaluate the statistical validity of the samples, the Relative ME was calculated for each of the quality attributes at the U.S. Aggregate and the three ECA levels. The Relative ME for the quality factor results was less than ±10% except for two attributes – stress cracks and stress crack index (SCI). While the lower level of precision for these quality factors is less than desired, these levels of Relative ME do not invalidate the estimates.
  • Two-tailed t-tests at the 95% confidence level were calculated to measure statistical differences between the 2011 and the 2012 quality factor averages.