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Is twin-row corn the next step?

In the early 1900s, when the primary power source for farmers was the horse, corn row spacing commonly ranged from 38 to 40 inches to accommodate the animal’s wider girth. While tractors eventually replaced the arguably more temperamental horses, row spacing didn’t change much until research in the 1960s showed narrowing it to 30 inches could increase corn yields by 5% or more. Over the ensuing years, many growers gravitated to narrower row spacing, making 30 inches the predominant planter configuration.

Coinciding with the decrease in row width, plant populations began to increase. Consider that, while average seeding rate for corn in the 1940s was around 10,000 plants per acre, many growers this year will be dropping 35,000 to 40,000 seeds per acre. That represents a 250% to 300% increase. The trend is to increase populations each year by about 400 plants per acre.

Plant populations are likely to continue increasing yearly with further stress-tolerant hybrids and the future promise of biotech “high-yield” genes.

Crowding is a concern

As seeding rates increase, in-row plant crowding is an emerging concern for both agronomists and growers. Can we continue to force more plants into a concentrated area within the row? Or do we need to consider narrower row spacing options to allow more equidistant spacing of plants?

In theory, many advantages exist with narrower row widths: can use same planter for corn and soybeans; increase the utilization of light; have more even plant-to-plant spacing and less in-row crowding; reduce weed competition; and have earlier canopy closure and soil shading. These advantages could allow plants to intercept more sunlight and nutrients and endure less stress, thus increasing yield.

Research in the northern Corn Belt has shown some advantage to narrower row spacing; however, work done in Iowa has been less conclusive. University and seed company researchers think the northern Corn Belt’s yield response may be due to the region’s shorter growing season and limited light compared to Iowa, where these factors seem less yield-limiting.

Iowa State University researchers have studied several narrow-row spacing configurations since 30-inch rows became the standard. Extensive work done from 1995 to 2000 comparing 15- to 30-inch rows showed no yield difference between the two. More recently, we have taken a long, hard look at twin-row corn.

In twin-row corn planting, two rows about 7 to 8 inches apart are placed on 30-inch centers. Besides the same potential advantages as other narrow-row systems, twin-rows have other theoretical advantages. Among them, growers may not have to make major modifications to sprayers and corn heads, and planter units place the seed more accurately because each is planting half as many seeds per acre.

Growers who use the twin-row system tell me that “theoretical” doesn’t always translate into “real.” A few of the twin-row challenges they have experienced are keeping equipment running true on side hills, harvesting lodged corn, watching ears flying off plants being pulled violently sideways 4 inches into the snap rolls, and keeping sprayers off the row. However, these row-spacing pioneers also tell me that, for the most part, they feel the benefits offset these challenges, and they plan to continue with their twin-row systems.

In the mid-2000s, staff and I at the ISU Armstrong Research Farm near Lewis, in southwest Iowa, did four years of work on twin-row corn. While results varied from year to year, by the end of the study we found no real yield differences between twin-row and 30-inch corn. In 2006, ISU Extension corn specialist Roger Elmore picked up our work and has continued the 30-inch to twin-row comparisons at various locations in Iowa.

Elmore and his crew improved on our protocols by looking at seeding rates ranging from 28,000 up to 48,000 kernels per acre. Again, field-scale, replicated work told us that, while there were year-to-year differences, the two systems yielded the same over several years.

Yield potential in Iowa

When do we expect to see narrow-row corn consistently increase yield potential in Iowa? As mentioned, plant populations generally increase every year. Much of the yield increases seen today with our modern corn hybrids come from their ability to withstand higher stress. One of the most important stresses modern hybrids are better able to withstand is higher plant-to-plant competition.

As plant populations significantly increase, we expect the yield differential to shift away from 30-inch rows toward narrower row systems. For today, we are confident the optimum row spacing in the central part of the Corn Belt varies from 15- to 30-inch row widths. Yes, I know, this is not a “firm” answer. In essence, right now if you pick a row spacing in that ballpark, you’ll be in great shape.

We’ll continue our work with narrow-row corn systems; in fact, Iowa State is working with some major seed companies in screening hybrids for responses to narrow-row spacing. Will the next predominant row configuration be 15 inch, 20 inch or twin row? Stay tuned!

McGrath is the partnership program manager of ISU’s Corn and Soybean Initiative.

This article published in the February, 2012 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.