Harvest Pressure Takes Hold in Corn Basis

The corn harvest in Illinois has begun, with the USDA estimating that 8% of the crop was already harvested as of September 14. As combines roll across the US 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.

A study by farmdoc daily examined seasonal corn basis patterns for 136 elevators across twelve Corn Belt states from 2010 to 2025. The results show that the average size of the dip in basis is about 11 cents per bushel, with a median harvest basis decline of 16 cents on average and 19 cents per bushel in Illinois.

The study found that the Corn Belt average basis bottoms in mid-October, when harvest pressure is greatest. Basis weakens as combines roll and harvest progress speeds up, reaching its low in the same week the crop crosses 50% harvested. The relationship between local harvest pressure and seasonal dip in basis is imperfect, with much of the difference attributed to given years.

The results suggest that harvest pressure has a geography, with basis falling furthest in the central and eastern Corn Belt. Locations close to river transport and closest to main flow of corn to end-users experience deeper harvest weakness.