Armstrong Research and Demonstration Farm
Current row widths employed by producers typically vary from 15 in. to 38 in., with most producers at 30 in. today. Yet more and more acres are being converted to narrower row widths(most often 15 in. or 20 in.). Numerous advantages exist with narrower row widths. These include using the same planting equipment for corn and soybeans, reduced weed competition, increased shading of the soil, increased light interception per plant, and less in-row crowding.
Iowa State University
Abendroth, Lori and Elmore, Roger W., "Row Spacing with Variable Seeding Rates" (2008). Iowa State Research Farm Progress Reports. 662.