How Row Spacng Affects Irrigated Soybean in Southwest Nebraska

Aerial image of field showing differences between 15-inch and 30-inch row spacings — Figure 1. TerrAvion aerial imagery taken on Aug 4, 2017 at Chase County site showing less vigor and higher thermal stress in 30-inch row soybeans than in 15-inch row soybeans.

April 27, 2018

Strahinja Stepanović - Former Extension Educator

Laura Thompson - Former Extension Educator

Keith Glewen - Extension Educator Emeritus

Continuous corn has been the most common and in many cases the most profitable irrigated crop sequence in southwest Nebraska. However, difficulties in managing resistant pests (Western corn rootworm, western bean cutworm) and bacterial disease outbreaks (Goss’s wilt, Bacterial leaf streak) have triggered the need for adding other crops, such as soybean, to irrigated crop rotations in southwest Nebraska.

Larger adoption of soybean, however, has not readily occurred in this area. For example, planted soybean acres in southwest Nebraska were 153,000 acres and 151,500 acres and average soybean yield was 55.8 bu/ac and 61.5 bu/ac for 2010 and 2017, respectively (USDA National agricultural statistics service).

On-Farm Research Study: 15-inch Versus 30-inch Rows

Soybean row spacing research in eastern and central Nebraska often has shown a potential to increase soybean yield with narrower rows (15-inch or drilled). In addition, many farmers from western Nebraska have reported superior soybean yield with 15-inch rows due to the faster rate of canopy closure, better weed suppression, and reduced evaporative loss early in the season (Figure 1); but limited data is available on what those yield differences may be.

In 2017, the Nebraska Soybean board funded an on-farm research initiative to quantify the yield differences between irrigated soybeans planted in 15-inch versus 30-inch rows in southwest Nebraska. We conducted three replicated on-farm studies comparing soybean yields in 15-inch vs 30-inch rows. Field experiments were carried out at one location in 2015 and two locations in 2017. Site descriptions, agronomic information, and data on percent grain moisture at harvest, yield (bu/ac), and marginal net return in dollars/acre ($/ac) for these studies is summarized in Table 1 (below).

For more information about soybean row spacing view the on-farm research results (PDF publication) or search the results database. If you’re interested in evaluating the impact of soybean row spacing on your farm in southwest Nebraska, contact Strahinja Stepanovic at 308-352-4340 or email sstepanovic2@unl.edu.

Also check the latest UNL recommendations on soybean planting dates and seeding rates.

Results

When averaged across site-years, soybean planted in 15-inch rows yielded 67 bu/ac which was 7 bu/ac more than soybeans planted in 30-inch rows (60 bu/ac). Yield differences ranged from 4 bu/ac in Chase County (2015, 2017) to 12 bu/ac in Perkins County (2017). Soybeans planted in 15-inch rows also had lower grain moisture at harvest (up to 0.9% less) and significantly greater marginal net return ($25-$128 per ac) than soybeans planted in 30-inch rows.

Aerial imagery at the Chase County site in 2017 showed less vigor and higher thermal stress in 30-inch row soybeans during the early reproductive growth. The on-farm research cooperator at the site also observed better suppression of volunteer corn with 15-inch rows.

Recommendations

Planting irrigated soybeans in 15-inch rather than 30-inch rows definitely showed a potential for southwest Nebraska farmers to increase soybean yield and profit.
Aerial imagery showed less thermal stress in 15-inch row spacing soybeans, which suggests that in cases where water may be limiting, such as in sandy soil with low water holding capacity and higher evaporative losses, there may be an even greater benefit to 15-inch row spacing. More research is needed to evaluate soybean yield response to narrower rows in heavier soils compared to sandier soils.

Notes

Although we have not observed differences in disease pressure in our studies, it has been reported that planting soybean in 15-inch rows may increase the occurrence of white mold disease.
Finally, switching from 30-inch to 15-inch rows would require either double planting or buying a 15-inch row planter.

Acknowledgements

Thank you to the Nebraska Soybean Board for funding row spacing and late season N-management research in southwest Nebraska. Also, thank you to our collaborators Leon Regier of Perkins County and Tim Varilek from Chase County for their time and effort to conduct row spacing studies in soybean and generate research-based information that could benefit many farmers in southwest Nebraska.

Table 1. Site description, agronomic information and data on grain moisture at harvest (%), yield (bu/ac) and marginal net return ($/ac) for irrigated soybeans grown in 15-inch and 30-inch row spacings at three site-years in southwest Nebraska.
Site Description	Perkins County (2017)		Chase County (2017)		Chase County (2015)
Soil type	Valent Loamy sand		Valent loamy sand		Valent loamy sand
Planting date	May 25		May 17		May 26
Harvest date	Oct. 28		Oct. 14		Oct. 12
Previous crop	Corn		Corn		Corn
Rainfall (inches)	12		15		11
Irrigation (inches)	13		13		13
Agronomic information
Tillage	No-till		Conventional		No-till
Variety	Curry® 1264		Asgrow® 2733		Asgrow® 2733
Maturity	2.6		2.6		2.6
Population (plants/ac)	120,000		145,000		160,000
Study results
Row spacing	15-inch	30-inch	15-inch	30-inch	15-inch	30-inch
Moisture at harvest (%)	12.6 B*	13.5 A	10.4 A	10.3 B	10.1 A	10.7 B
Yield (bu/acre)†	61 A	49 B	62 A	58 B	78 A	74 B
Marginal Net Return‡ ($/ac)	553 A	425 B	545 A	520 B	694 A	659 B
*Values with the same letter are not significantly different at a 90% confidence level. †Bushels per acre corrected to 13% moisture. ‡Marginal net return based on $8.90/bu soybean.