Corn Harvest Pressure Erodes Basis by 11¢ per Bushel

The corn harvest has begun in Illinois, with the USDA estimating that 8% of the crop was already complete by September 14. As combines roll across the U.S. Corn Belt, commodity market analysis often attributes any observed decrease in crop prices to 'harvest pressure'. This phenomenon occurs when abundant supply at harvest means farmers are willing sellers and grain buyers less aggressive bidders in the market for immediate delivery.

Researchers studied seasonal corn basis patterns from 2010 to 2025 across 136 elevators in twelve Corn Belt states. They found that the average size of the dip in basis is about 11¢ per bushel, but this masks greater seasonal variation in specific locations. The bottom of the harvest low arrives at different weeks and depths in different places.

The researchers discovered a strong connection between the timing of the harvest low and the availability or supply of grain to the market. Basis weakens as combines roll and harvest progress speeds up, reaching its low in the same week the crop crosses 50% harvested.