Smaller-than-expected corn and soybean supplies are also contributing to the unusual harvesttime rally.

After struggling through most of 2020, corn and soybean futures markets have surged sharply higher over the past two months thanks to smaller-than-expected supplies combined with strong demand in both the domestic and export markets, crop market analysts said.

New-crop December corn futures neared $4.20 per bushel last week, up nearly $1 per bushel from the price levels in early August, just before the crop futures markets began to catch fire. 

The trend in soybean futures prices is just as strong. New-crop November soybean futures prices topped...