INSIGHTS
- Planting soybeans in narrow rows takes advantage of light utilization and can provide improved weed control.
- The benefit of planting soybeans in narrow rows at a lower seeding rate may not always be as great as when planting 140,000 seeds/A.
- Varying levels of yield increases at both seeding rates were seen in 30-inch and 15-inch rows.
Introduction
The majority of soybean acres are planted in either 15-inch or 30-inch row spacing across the growing regions, but the predominant row spacing varies significantly by state. For example, 69% of the soybean acres in South Dakota are typically planted in 30-inch rows compared to 5% in Ohio, whereas these states plant 15% and 89% of their acres in row spacings of 15-inches or less, respectively.1
Row spacing trends are often influenced by factors other than yield. Equipment purchases in areas where cropping options are more diverse are often more aligned to crops with unique row spacing like cotton or sugar beets, which favor wide and narrow rows respectively. Areas with disease complexes that thrive in moist, wet environments often encounter white mold more frequently and likewise tend to use wider row spacing as a preventive measure. Yet numerous trials often demonstrate yield benefits from narrow row spacings in areas predominantly planting wide rows. This preference is likely driven by the desire to achieve maximum light interception prior to early reproductive stages (Figure 1).2
2024 Soybean Row Spacing Trials
To better understand seeding rate influence on row spacing response, trials were planted at Waterloo, NE, and Malta, IL, in 2024. These trials compared four varieties planted at 100,000 and 140,000 seeds/acre in both 30-inch and 15-inch row spacing. Both trials were planted in the last week of April. Varieties with differing plant height and canopy type were intentionally chosen to help understand if varietal responses differ.
* = significant (P=0.10) row spacing response within the specified seeding rate
Graph 1. Soybean yield response to seeding rate and row spacing from 2024 trials.Results
* = significant at p=(0.10) level
Table 1. Soybean variety yield response in 15-inch rows in 2024 trial.Narrowing row spacing from 30 to 15 inches resulted in varying levels of yield increases at both low (100,000) and normal (140,000) seeding rates. At Malta, there was a 1.7 and 3.7 bushel per acre (Bu/A) response to narrow rows within the low and normal seeding rates respectively (Graph 1). A response to narrow rows was only observed within the lower seeding rates at Waterloo, NE (3.8 Bu/A, Graph 1). The two locations responded very differently to overall reductions in seeding rates. Both seeding rates yielded similarly in wide rows at Malta, although there was a 2.2 bushel yield penalty with reduced seeding rates in narrow row configuration. However, at Waterloo there was a yield loss of 7.8 Bu/A with reduced seeding rates in wide rows, whereas reduced and normal seeding rates yielded similarly in narrow rows.
Individual variety responses to narrow rows ranged from zero to 5.9 Bu/A depending on the variety and location (Table 1). There was no repeatable trend across locations to indicate specific varieties were more likely to respond to narrow rows.
Summary
Like historic trials, these trials demonstrated incremental yield potential through narrow row spacing. They also indicate that yield benefits from narrow rows can still be observed at lower seeding rates, yet the benefit may not always be as great as when using more normal seeding rates (140,000). There are multiple factors going into equipment purchase decisions that may outweigh yield benefits seen in this trial. However, in addition to yield, growers should also consider the added benefits associated with narrow rows such as faster crop canopy, improved leaf-light interception, improved weed control and weed soil seed bank management.
Figure 1. Canopy closure differences between 30-inch and 15-inch row spacing on July 31, 2024 at Malta, IL.References
1USDA-NASS, 2015 Crop Production Survey.
2Board, J.E., and B.G. Harville. 1992. Explanations for greater light interception in narrow- vs. wide-row soybean. Crop Sci. 32:198-202
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