The U.S. Department of Ag­­riculture (USDA) last week slashed almost 5 bushels per acre from its earlier trend-based projection of U.S. average corn yields for 2021 as extreme drought conditions hammer crops in the western Corn Belt, offsetting record yields east of the Mississippi River.

While projections for 2021 top last year, the uneven impact of weather on this year's crop is substantial.

“It’s ...