Narrow Corn Rows Increasing Yield Potential in Northern Latitudes

• Narrow row corn has shown increased yields consistently in northern latitudes but less consistently when moving south.
• Response to 20” rows was inconsistent across locations as well as between hybrids in 2019 trials.
• Individual hybrid response to seeding rates in 20” rows was similar to 30” rows. 
• Previous 30” hybrid seeding rate characterization data is still relevant for creating 20” seeding prescriptions.

Figure 1.  Row width influence on seed spacing within rows at 35,000 seeds per acre.

Corn row spacing has evolved over time in response to equipment innovations that have slowly enabled narrowing rows. Early corn fields were planted in 40” rows to accommodate the width of a horse, not because 40” rows resulted in the greatest yield. With the introduction of the tractor, corn row spacing slowly began to evolve from 40” to present day standard 30” rows. Each transition to slightly narrower rows by equipment manufacturers simultaneously increased in-row seed spacing as illustrated in Figure 1. Greater distances between plants helps reduce interplant competition for resources and achieves a more complete canopy across rows. Improved canopy closure helps conserve soil moisture, but also makes the corn plant more efficient at capturing and utilizing light for photosynthesis.¹ Increased seed spacing also provides an opportunity for corn breeders to develop hybrids that can better withstand the interplant competition of increased seeding rates. The ability to plant and harvest more ears per acre combined with improved stress tolerant genetics has enabled continuous yield gains year after year.

Is there opportunity to reduce corn row spacing more?
The physiological principles of these yield gains continue to test the possibility of further increasing yields with narrower rows. Soybeans have consistently yielded higher in 15 to 20” rows, posing the question of the overall value of switching an entire farm operation to narrower rows.
Advantages will likely only occur if a yield limiting factor is minimized due to narrowing rows. Sunlight is not often considered a yield limiting factor in most geographies. Northern latitudes have shorter growing seasons, but also receive sunlight at a lower angle throughout the summer and this sunlight is spread over a greater surface area. Minnesota, North Dakota, and Michigan geographies are more limited in sunlight, making light interception a yield limiting factor in these latitudes.²

Previous Findings
Previous studies examining row spacing have shown that while narrower rows do not always yield higher than standard rows, they often result in a small advantage in northern latitudes. Widdicombe and Thelan (2002) found that 15” rows yielded 6% better than 30” rows at several sites in Michigan. Similarly, Porter and colleagues (1996) observed a 7-8% yield increase with narrow rows at several sites in Minnesota. Results from Iowa have been less consistent with a 2% yield reduction in narrow rows4 although sometimes narrow row advantages in higher yielding environments (greater than 235 bu/A) have been observed.⁵

Previous row-spacing studies using multiple hybrids, found them all to respond similarly across row spacings. However, Farnham et al. found 2 of 6 hybrids that performed better in 30” rows and one better in 20” rows.

Agronomy in Action Trials
Before adopting narrow row spacing, it is important to address the following 3 questions: 

1. Are there advantages or shortcomings to growing corn in less than a 30” row spacing? 
2. Do seeding rates need to increase for 20” rows?
3. Do some hybrids respond differently or require different management in 20” rows?

Figure 2.  2019 20” row spacing trials

Golden Harvest^® Agronomy In Action research implemented trials to test how hybrids respond to changing row spacing and seeding rates. Over 46 different hybrids were evaluated in 20” and 30” row spacings at 5 different seeding rates ranging from 26,000 to 50,000 seeds/A across 5 locations. Locations shown in Figure 2 ranged in latitude from Slater, IA (latitude of 41.88) north to Bird Island, MN (latitude of 44.7). Trials were well-fertilized and received sufficient rainfall, limiting any potential differences to be contributed to amount of sunlight intercepted.


 Graph 1.  Rowspacing response by location

Trial Results
Yield response to row spacing was inconsistent across locations. Response to 20” rows ranged from -7 bu/A to +12 bu/A, averaging a 2 bu/A increase across all sites. When yield was averaged across corn populations, Bird Island had greater yields with 30” rows, Nerstrand had higher yields with 20” rows as shown in Graph 1. The 3 other sites only found row spacing differences at specific populations.

Yield response to row spacing varied by population at every location. Graph 2 illustrates how the optimum seeding rate and narrow row advantage changed dramatically across 2 locations. Lower planting rates with narrow rows increased in-row seed spacing resulting in a loss of narrow row efficiency for capturing solar radiation. On the other hand, populations at 50,000 plants/A likely experienced enough in-row competition that changes in the between-row environment were not meaningful.

Graph 2. Row spacing response change across 2 locations.

Individual hybrid response to narrow rows was also extremely inconsistent across testing locations. Many times, there was little difference in yield within each hybrid when comparing the 2 row spacings at optimum seeding rates. G02K39 provides a good example of inconsistent hybrid response to narrow rows (Graph 3). Twenty” row spacing improved yields at Bird Island while 30” rows maximized yields at Nerstrand. In both situations, the optimum seeding rate remained unchanged at both locations no matter what the row spacing, implying that increasing seeding rates with narrow rows may not be necessary with all hybrids.

It is difficult to test the interaction of row spacing and row orientation with a limited number of sites, but it is interesting to note that the 3 sites planted with east-west orientation (Bird Island, Winthrop, and Stanton) ranged from mostly favoring 30” rows to one small advantage for 20” rows, while sites planted in a north-south orientation (Nerstrand and Slater) both favored 20” rows, sometimes with a significant advantage.


Graph 3.  Example of inconsistent hybrid response to narrrow rows.

Should you make the switch?
Narrower corn rows have been shown to increase yields more times than not in northern latitudes but making the switch to narrower rows in these latitudes should still be considered in context of the entire farming operation. If you are planting other crops that respond consistently to narrow rows, such as soybeans or sugar beets, there can be significant yield gains for those crops and very little risk of losing corn yield.

Net yield gains for narrowing row spacing of these crops may be sufficient for switching even without corn yield gains, no matter the latitude. The opportunity to increase corn seeding rates in 30” rows will eventually be capped due to in-row seed spacing limitations, leaving narrow rows and focused breeding of genetics that tolerate crowding as the only chance for continued seeding rate increases in future years.

When switching to narrow rows, individual hybrid seeding rates can be managed similarly in narrow and wide rows and should not require significant increases over current practices. Utilizing narrow row corn as part of an overall intensive management system that includes increasing seeding rates, fungicide application, irrigation and high soil fertility levels has merit for increasing yield potential. Utilizing narrow rows and increased seeding rates in lower yield potential fields or fields at high risk of stress such as drought or disease may not be a good combination. Planting in narrow rows in a north-south orientation may also increase solar capture and potentially yield, but this decision should be weighed with other row orientation factors, such as wind vulnerability.

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References:
1 Westgate, M., F. Forcella, D. Reicosky and J. Somsen. 1997. Rapid canopy closure for maize production in the northern US Corn Belt: radiation-use efficiency and grain yield. Field Crops Research 49:249-258.
2 Porter, P., D. Hicks, W. Lueschen, J. Ford, D. Warnes and T. Hoverstad. 1997. Corn response to row width and plant population in the northern Corn Belt. J. Prod. Agric. 10:293-300.
3 Widdicombe, W. and K. Thelen. 2002. Row width and plant density effects on corn grain production in the northern Corn Belt. Agron. J. 94:1020-1023.
4 Farnham, D. 2001. Row spacing, plant density, and hybrid effects on corn grain yield and moisture. Agron. J. 93:1049-1053.
5 Licht, M., Parvej, M. and E. Wright. 2019. Corn yield response to row spacing and plant population in Iowa. Crop, Forage, & Turfgrass Management. 5:0032. doi:10.2134/cftm2019.05.0032