Ever since the replacement of horse-drawn machinery allowed corn rows to be less than 40 inches apart, growers and researchers have looked to narrower row spacing as a way to increase corn yields. Today, the vast majority of U.S. corn acres are grown in 30-inch rows with narrow rows being defined as any spacing less than 30 inches.
Plants in narrow rows are more equally spaced within and across rows. Researchers are studying whether more equidistant plant spacing will consistently increase corn yields and if certain growing environments are better suited for narrow rows.
DuPont Pioneer has conducted numerous narrow-row and twin-row studies throughout the Corn Belt to evaluate the effects of narrow rows on corn yields.
The most consistent positive responses were found in the northern Corn Belt states of Michigan, Wisconsin, Minnesota, North Dakota, and South Dakota where the average yield advantage in narrow rows was 2.7% (Figure 1). In the central Corn Belt, the narrow-row advantage averaged 1% across all the locations tested.
A 2-year DuPont Pioneer/University of Minnesota study also showed a yield advantage with 22-inch rows compared to 30-inch rows in northern Minnesota. Results indicated that narrow rows were advantageous at higher seeding rates. When plant population was increased from 33,000 to 38,500 plants/acre, yield increased by 4% in 22-inch rows (Figure 2).
Twin-row planting is another row configuration that has gained interest as a way to increase plant-to-plant spacing and avoid some of the difficulties and costs of switching to narrow rows.
Pioneer conducted research studies at several Midwest locations, comparing yield in twin and 30-inch rows at plant populations of 36,000, 42,000 and 48,000 plants/acre. These studies did not show a yield advantage for planting twin rows over 30-inch rows at any population (Figure 3).