Comparison of 20-inch versus 30-inch Corn Row Widths

The row width debate comparing narrow row corn (20 inches or less) to 30-inch rows has been occurring for over a couple of decades. Seventy-five years ago, the question was whether to move from 40-inch rows to 36-inch rows. With the advent of the tractor versus the horse to pull equipment, the row width configuration became more flexible. Shortly after this change to tractors, the switch to 30-inch rows occurred in the central and north growing corn regions of the US. So, is it now time to move from the standard 30-inch row to a 20-inch or narrower row spacing?

To support the discussion for moving to a narrower row, a review of research in the subject area will be useful. The first data point to consider is an Iowa State University study that included 10 site-years and was conducted from 2009 to 2016. In this study, 50% of the time, 20-inch rows yielded 4.8 to 15.9 bu/acre more than 30-inch rows. The remaining 50% had no yield difference.¹ In other Iowa State University studies, there was a clear indication that 20-inch rows had a yield advantage over 30-inch rows but only in high yield environments. To better define this difference, in yield environment of 235 bu/acre or more, a yield increase of 8 to 10 bu/acre was observed for the 20-inch rows versus the 30-inch row width. In yield environments of 180 bu/acre or less, 20-inch and 30-inch row widths had similar yields.²

In a 2020 Bayer Crop Science study conducted in Iowa, 48 corn products were evaluated in two locations at 20-inch and 30-inch row spacings and included planting rates of 30,000, 35,000, and 40,000 seeds/acre in each location and row width. When yield results were averaged across all products, there was no overall yield difference between the two row widths.

Possible explanations for the yield response to narrower rows include:

1. Potential yield increases due to narrow rows have been more consistent in northern regions.
2. Variability in narrow row production can occur from year to year.
3. Corn product selection and population are important considerations with respect to row width.

Yield response to narrower rows versus 30-inch rows in northern growing regions are because of the shorter growing season and less available growing degree days which normally results in a shorter stature plant with fewer leaves.³

Another example of yield increases in narrow row corn is a study done in northeast Nebraska. Over a 3-year period 20-inch rows had 4% more grain yield than 30-inch rows.⁴ A closer look at the data by year, shows an increase in yield for 20-inch versus 30-inch in two of the three years of this study. The explanation from the researcher pointed toward more heat units earlier in the season which led to greater plant growth earlier in the year and more light interception, negating the need for narrower rows.⁴

A 1996 University of Wisconsin article summarizes the results that reinforce this north to south response difference.⁴ Yield response to narrower row corn was 9.9% increase in Minnesota and 8.8% increase in Michigan when compared to 30-inch rows. In the central Corn Belt, responses to narrow rows decreased to 3% in Illinois and 2.7% in Indiana but the response was extremely variable and inconsistent.⁵

After this data review, considering the question of 30-inch rows versus row widths of 20-inch or less in corn, the decision to make changes in an individual’s operation depends on many factors including:

1. Geography - Yield increases from narrower row corn were more consistent in northern corn growing areas with a shorter growing season and fewer GDUs.
2. Yield environment - Higher yield environments showed more response to narrower rows.
3. Equipment - Moving from 30-inch to 20-inch rows would require changes or modifications in planters and harvest equipment which would add cost to an operation. The additional investments would need to be recovered by increased yields and net profit.
4. Leaf area - with the narrower rows, there is an increase in the leaf area especially early in the growing season. This extra leaf area could help shade the ground which in turn could reduce soil evaporation and possibly help with weed control. The other side of this argument is with the increased leaf area, in hot, dry conditions, the amount of leaf transpiration would increase due to more leaves absorbing sunlight. The weed management argument makes some sense but in a meta-analysis done by University of Nebraska-Lincoln, they found that narrow rows were beneficial for weed control in soybean production but did not have the same beneficial effect in corn production.⁶
5. Soybean production - The purchase or modification of equipment to plant narrow row corn might benefit the operation’s soybean acres more than the corn. This is part of a larger discussion on narrow row soybean production.
6. Management - The movement from a 30-inch row corn system to narrower rows may result in management changes including:

• The maturity and type of corn products used in the operation may need to be changed.
• Post application of herbicide, fertilizer, or other management products becomes more of a challenge to avoid plant damage in narrower rows.
• Equipment used in planting and harvesting narrower rows is heavier for the same given area as a 30-inch row system which increases the potential for soil compaction.

The move from a 30-inch row corn system to a 20-inch row system can have its advantages for some farming operations but many factors need to be considered before making any changes to help ensure this change is right for each individual operation (Figure 1).

Channel Agronomist
Steven Troesser

Sources

¹Wright, E. and Licht, M. 2018. Corn row spacing considerations. ICM News. Integrated Crop Management. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/cropnews/2018/03/corn-row-spacing-considerations#:~:text=The%20results%20from%20this%20data,and%2030%2Dinch%20row%20spacing.

²Licht, M. Row spacing for corn. ICM News Encyclopedia Article. Integrated Crop Management. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/encyclopedia/row-spacing-corn-0.

³Stahl, L., Coulter, J, and Bau, D. 2009. Narrow row corn production in Minnesota. University of Minnesota Extension. Publication No. M1266 2009. https://extension.umn.edu/corn-planting/narrow-row-corn-production-minnesota.

⁴Shapiro, C.A. and Wortmann, C.S. 2006. Corn response to nitrogen rate, row spacing, and plant density in Eastern Nebraska. Agronomy Journal. American Society of Agronomy. https://acsess.onlinelibrary.wiley.com/doi/full/10.2134/agronj2005.0137.

⁵Lauer, J. 1996. Planting corn in rows narrower than 30-inches. Agronomy Advice. University of Wisconsin Agronomy Department. https://corn.aae.wisc.edu/AA/A008.aspx

⁶Singh, M., Thapa, R., Singh, N., Mirsky, S.B., Acharya, B.S., and Jhala, A. 2024. Does narrow row spacing help suppress weeds and increase yields in corn and soybean? CROPWATCH. Institute of Agriculture and Natural Resources. University of Nebraska-Lincoln. https://cropwatch.unl.edu/2024/does-narrow-row-spacing-help-suppress-weeds-and-increase-yields-corn-and-soybean/

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