Narrow Row Soybeans: Worth the Squeeze?

In the last decade or so, many farmers in southeast PA switched from planting soybeans at 30-inch row spacing to 15-inch or narrower. However, the conventional 30-inch row spacing is still the most common in other regions of the state. Research has found that narrower rows can improve early-season growth rates, weed suppression and overall yields. However, they aren't suitable for all circumstances, and farmers should consider several factors when deciding what spacing is best for their operation.

How does row spacing affect soybean growth and development?

When soybeans are planted in narrower rows at the same plant population (with more space between individual plants within a row), each plant has more space to spread laterally, both above and below ground, in a more uniform distribution (Figure 1). As a result, narrow row soybeans intercept a greater fraction of incoming light for photosynthesis early in the soybean growth cycle, when the canopy is not yet closed. Underground, the more uniform root distribution means better access to water and minerals and lower risk of erosion. Further, a more uniform plant distribution results in earlier canopy closure, which helps shade out weeds.

How does row spacing affect yield?

In a large study conducted in the US Midwest and South on full-season soybeans, narrow-row soybeans (≈15 inches) outperformed wide rows (≈30 inches) about 75% of the time, with an average 7% yield increase [Figure 2, Andrade, Rattalino Edreira ¹]. Data from producer surveys did not indicate a significant yield difference between narrow and wide rows, but researchers attributed this to confounding factors, such as narrow-row soybeans often being associated with late planting and other management practices that can decrease yield. Recent studies in the Mid-Atlantic have also found that 15-inch rows yielded higher than 30-inch rows ^{2, 3}.

While most studies agree that 15-inch soybeans can yield higher than 30-inch soybeans, there are mixed results on whether 7.5-inch soybeans provide a yield advantage ^{4, 5}. A key complication with comparing 7.5 with 15 and 30-inch rows is that 7.5-inch soybeans are typically planted with a drill, which has poorer singulation than a planter, and thus, results are confounded by differences in planting technology.

When are narrow rows a good choice?

Since the primary benefit to narrower rows is greater light absorption in the early growing season, they are useful in situations where accelerated growth is desired early in the season (from emergence to pod set). These include:

• Late planting, including double-cropping systems
• Earlier than recommended maturity group varieties
• High weed pressure

All of the above constrain early season growth and can reduce yields. Not surprisingly, data suggest that the yield benefit from narrow row soybeans is most pronounced in areas yielding 45 bushels per acre or less ¹.

The benefit of narrow rows under high weed pressure was demonstrated in a large study that summarized data from 11 US states, including several from the Mid-Atlantic region. Results showed that when only one herbicide application was made (either pre- or post-emergence), narrow rows (<30 inches) yielded higher than wide rows (30 inches). However, yields were not different when two herbicide applications were made ⁶.

When are narrow rows not a good choice?

There are certain situations where narrow-row soybeans are not feasible or do not provide a yield advantage, and in some cases they even reduce yield compared to 30-inch rows. For example:

• Narrow planting is unsuitable for systems that rely on inter-row cultivation, common in organic systems.
• Narrow rows generally do not provide a yield advantage over wide rows in high-yielding environments where weeds are effectively controlled, and early-season growth is not constrained.
• Fields experiencing severe drought stress, especially during the late soybean growth stages, are particularly liable to see reduced yields with narrow rows. This happens as a side effect of narrow rows improving water use early in the season. Once this water is taken up during the vegetative soybean stage, little remains in the soil during pod fill, when the plants require it most, resulting in lower yields.

Other considerations: equipment, wheel tracks, and white mold

Equipment considerations are important for deciding whether narrow rows will be practical and profitable for a given farm. Consider your rotation program – do you use the same 30-inch planter for corn and beans in alternating years? A 2008 economic analysis concluded that for purchasing a 15-inch split-row planter to be profitable, a farm with only a corn-soybean rotation would need to plant at least 355 acres of all crops combined, with at least half in soybeans, and see a soybean yield benefit of at least 1.9 bushels per acre ⁷. Due to economies of scale, the necessary increase in yield will shrink with higher-acreage farms. Of course, you will need to consider current commodity prices, equipment costs, and your farm's projected yields before deciding whether to invest in such equipment. Another consideration when switching to narrow rows is wheel track damage, which increases as row spacing decreases. However, research comparing 15- and 30-inch soybeans showed that the total damage incurred (a 1-6% loss) with narrower rows tends to be outweighed by the increase in yield ^{8, 9}. Lastly, the greater early canopy development with narrow rows can increase the risk of white mold, a disease favored by cool, damp microclimate. As with wheel damage, however, the damage caused by white mold in narrow row soybeans is typically outweighed by the narrow row yield advantage, except in very severe infestations. Research from North Dakota State found that planting wide rows (28 or 30-inch versus 22.5-inch or narrower) is only justified if at least 50 percent of the plants in the field show signs of white mold by the end of the season ¹⁰.

Conclusion

Planting soybeans at narrower spacings has the potential to increase yield in most, but not all, circumstances. In general, narrow rows are well-suited to several scenarios: late planting, high weed pressure, constrained early-season growth, and larger farms. It's important to identify the main factors limiting yields in your fields and the cost of your equipment before deciding whether switching to narrower rows is practical for any individual operation.

References

¹ Andrade JF, Rattalino Edreira JI, Mourtzinis S, Conley SP, Ciampitti IA, Dunphy JE, Gaska JM, Glewen K, Holshouser DL, Kandel HJ, Kyveryga P, Lee CD, Licht MA, Lindsey LE, McClure MA, Naeve S, Nafziger ED, Orlowski JM, Ross J, Staton MJ, Thompson L, Specht JE, Grassini P: Assessing the influence of row spacing on soybean yield using experimental and producer survey data. Field Crops Research 2019, 230:98-106.

² Cox WJ, Cherney JH: Growth and Yield Responses of Soybean to Row Spacing and Seeding Rate. Agronomy Journal 2011, 103:123-8.

³ Miller JO: 2024 Soybean Row Spacing and Population Studies for Coastal Soils. University of Delaware Weekly Crop Update, 2024.

⁴ Kratochvil RJ, Pearce JT, Harrison Jr. MR: Row-Spacing and Seeding Rate Effects on Glyphosate-Resistant Soybean for Mid-Atlantic Production Systems. Agronomy Journal 2004, 96:1029-38.

⁵ Kleczewski N, Kness A, Koehler A: Impacts of Row Spacing and Fungicide Timing on Foliar Disease, Greenstem, and Yield in Double-Cropped Soybeans Grown in the Chesapeake Bay Region of the United States. Plant Health Progress 2022, 23:243-4.

⁶ Singh M, Thapa R, Singh N, Mirsky SB, Acharya BS, Jhala AJ: Does narrow row spacing suppress weeds and increase yields in corn and soybean? A meta-analysis. Weed Science 2023, 71:520-35.

⁷ De Bruin JL, Pedersen P: Effect of Row Spacing and Seeding Rate on Soybean Yield. Agronomy Journal 2008, 100:704-10.

⁸ Hanna SO, Conley SP, Shaner GE, Santini JB: Fungicide Application Timing and Row Spacing Effect on Soybean Canopy Penetration and Grain Yield. Agronomy Journal 2008, 100:1488-92.

⁹ Holshouser DL, Taylor RD: Wheel Traffic to Narrow-Row Reproductive-Stage Soybean Lowers Yield. Crop Management 2008, 7:1-7.

¹⁰ Wunsch M: Key management considerations for soybeans in fields where white mold is a concern. North Dakota State University Extension, 2026.