Since the early 1970s, average row spacing in Ohio decreased from about 35 inches to about 30 inches in 2015. This reduction in row spacing coincided with an increase in average plant population from approximately 18,000 plants per acre to nearly 30,000 plants per acre. Due to considerable interest in narrowing row spacing even further, many university and seed company studies have compared corn planted in narrow rows (row spacing 22 inches or less) and conventional 30-inch row spacing.
Although narrow row systems are often perceived as a proven method for increasing yield and profitability, studies on narrow-row corn production have produced mixed results. Some of the inconsistency may be related to latitude with narrow rows in the North Central Region of the U.S. exhibiting the largest yield increases (2 to 3 percent or more) over 30-inch rows. This advantage diminishes moving southward with little or no yield advantages for narrow rows in the central Corn Belt. Results of a Michigan State University study conducted in 1998-99 showed that corn grain yields increased by 2 percent and 4 percent when row width was narrowed from 30 inches to 22 inches and 15 inches, respectively. However, in university research in central Corn Belt states (Iowa, Illinois, and Ohio) the yield advantage of narrow rows over 30-inch row spacings has been smaller (usually less than 2 percent) and less consistent. When they occur, yield increases with narrow rows have been found to occur at both moderate and high plant populations and at high and moderate yield levels. University of Illinois research found no trend for higher or lower yielding sites to show more response to narrow rows. Hybrids varying in maturity and plant architecture have generally exhibited yield responses to narrow rows similar to those for 30-inch row spacing. Some companies have marketed hybrids for high populations and narrow rows but university trials have not shown that these hybrids have an advantage over high yielding hybrids in 30-inch rows.
Some growers are considering twin rows as another row spacing configuration that may offer some of the yield increases associated with narrow row corn. In the typical twin row system, two rows are placed 6 to 8 inches apart on 30-inch centers, although other twin row configurations are used. Twin rows make it possible to create narrow rows without changing the row configuration of other equipment, and to avoid costs associated with equipment conversion to a narrow row system. Staying on 30-inch centers allows growers to use the same corn header and tractor tire spacing used in 30-inch corn production. In recent university studies, results have generally indicated little or no advantage for twin row system compared to 30- inch row spacings.
Narrowing row spacing below 30 inches has usually proven advantageous in silage corn production. Studies at Pennsylvania State University indicate a 10 percent advantage for silage production using 15-inch or 20-inch rows compared to 30-inch rows.
Potential yield gains from narrow rows must be balanced against the investment for new equipment and higher input costs associated with narrowing row spacing. Key changes for narrowing rows include tractor and combine rims and tires, combine heads, and planter modifications. Greater interest in increasing equipment use efficiency by using the same planter or drill for soybean, sugar beet and corn may warrant adoption of narrow row systems for corn. Producers in northern regions that also grow soybeans and sugar beets in 22-inch rows often find it more efficient to use this same row spacing for corn.