Northwest and Allee Research and Demonstration Farm
Over the past several decades there has been a shift in corn row spacing from the traditional 40-in. rows that were needed so horses could fit between the rows, to 38-in., 36-in., and the most popular 30-in. rows. The narrow row spacing usually has resulted in increased yields due to it allowing more space between the plants within the row. More recently there has been interest in seeing if a narrower row spacing (15-in. or 20-in.) will further increase corn yield.
Iowa State University
Fawcett, Jim; Licht, Mark; Sievers, Josh; and Rogers, Jim, "On-Farm Corn Row Spacing Trials" (2015). Iowa State Research Farm Progress Reports. 2126.