Narrow advantage for narrow rows
In theory, corn should be grown in rows less than 30 inches apart. That's because in narrower rows the plants are farther apart within the row and, therefore, compete less with each other for light, water, and nutrients. Equidistant planting would seem ideal.
In reality, however, there usually isn't much yield difference between 30-inch rows and narrower rows except in the northern Corn Belt and in other regions when fertility or water are in short supply.
“Narrow rows may be most beneficial where canopy development and yield are challenged by marginal soils or climates,” says Purdue University agronomist Bob Nielsen. He offers five examples.
● Northern climates where it is cooler and there is less growth.
● Nutrient-deficient soils, especially if nitrogen is lacking.
● Sandy, nonirrigated, often droughty soils.
● Shorter-season hybrids.
● Smaller, shorter, less leafy hybrids.
Silage corn also does well in row widths less than 30 inches.
Narrow rows give individual plants a lot more space. At a population of 36,000, individual plants in 30-inch rows are 5.8 inches apart within the row. At that same population, plants in 20-inch rows are 8.7 inches apart within the row, while plants in 15-inch rows are 11.6 inches apart. Plants in twin rows (8 inches apart on 30-inch centers) are also 11.6 inches apart within the row. If the plants in the twin rows form a diamond, there are 9.9 inches between plants in adjacent rows. (See the diagram on page 52.) The corn on the opposite page is in 15-inch rows.
According to most research and farmer experience, narrow rows (less than 30 inches) usually yield better than 30-inch rows north of Interstate 90, which runs a few miles north of the Iowa/Minnesota border. University of Minnesota agronomists say research in southern and central Minnesota shows that corn in 20-inch rows can increase grain yields by up to 7% to 9% compared to 30-inch rows.
Greg Stewart, a corn specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, says research in the 1990s showed twin rows could outyield 30-inch rows and were sometimes equivalent to 15- and 20-inch rows. However, there was no yield difference at some sites. When the results from several studies at several populations and in several locations were averaged, twin-row corn yielded 6 bushels better in Canada. That was a 5% to 6% increase over 30-inch rows.
But across the heart of the Corn Belt, yield advantages are typically small and inconsistent, unless there are water and nutrient issues. (Most likely, the majority of row-width research has been done in medium- or high-yield environments.) However, there is rarely a yield penalty for using narrower row widths or twin rows. That's an important consideration for farmers who want to grow other crops, most notably soybeans, in narrow rows.
Nielsen says, “Thirty-inch rows are not a primary limiting factor for corn grain yield today in the heart of the Corn Belt. If there is more than enough water, nutrients, and light, then you are not likely to see a significant response to narrower rows.”