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Row Spacing in Soybeans

24 March 2014

Monsanto

The combination of optimum genetics and good agronomic practices along with favorable environmental conditions are required to help increase yield potential.

Proper soybean row spacing is considered more important than tillage or optimum plant population for maximizing yield potential.

Narrow row spacing (less than 30-inch) has been expanding rapidly in the past 20 years. Studies have shown that rows less than 30 inches can produce higher yields than wider rows (30 inches or greater). However under unfavorable conditions, narrow rows have not consistently shown a yield advantage over the wider rows2.

Twin row planting has been shown to have several potential benefits including maximizing light interception and allowing for greater plant root growth and development, which increases water and nutrient uptake.

Testing was done to demonstrate the impact of different row spacing configurations on soybean yield potential under various growing conditions, such as the unusual drought and heat stress conditions of 2012.

Materials and Methods

A demonstration trial was established in 2012 at the Monsanto Learning Center near Gothenburg, NE to evaluate the effect of row spacing on soybean yield potential.

A Genuity® Roundup Ready 2 Yield® soybean product with relative maturity (RM) of 2.4 was planted on 7 May 2012 in 7.5-inch (drilled), 15- and- 30-inch row, and 30-inch twin row systems. In all row widths, the planted population was 140,000 seeds per acre.

The trial consisted of 16 plots (four row widths, one soybean product, four replications), which were conventionally tilled on 2 April 2012. The plots were planted into previous corn ground.

Enlite® (2.8 fl oz/acre), Roundup PowerMAX® (28 fl oz/acre), and Sharpen® (2 fl oz/acre) herbicides were applied pre-plant on 23 April 2012. In addition, Roundup PowerMAX® (28 fl oz/acre) and Warrant® Herbicide (2 pints/acre) were applied on 2 July 2012. Between 1 June and 10 September 2012 approximately 16 inches of irrigation were applied to all plots at a rate of one inch/acre on weekly intervals. All plots were harvested on 25 September 2012. Other agronomic practices were in alignment with local standards.

Weather conditions during the 2012 growing season were considered to be abnormal for the area with low rainfall and unusual high temperatures (Figure 1). Generally, May, June, and July temperatures were 9, 11, and 7 degrees, respectively, higher than 2011. There were days in late June and early July 2012 that daytime temperature was at or above 100° F; 26 June temperature recorded 111° F.


Figure 1. Average maximum temperature and rainfall from 1 May to 31 October for 2011 and 2012.

In 2011, only two days in late July when daytime high temperatures were 100° F, while 16 days of temperature at or above 100° F was recorded in 2012.

The rainfall in 2012 was below the 2011 level. Only 11 inches of rainfall was received from May to the end of October compared to 26 inches at the same time period in 2011.

Results and Discussion

Results showed that out of the four planting configurations, the drilled 7.5-inch row outperformed the 30-inch rows. The 7.5-inch row produced an average 92 bu/acre, while the 30-inch row yielded the lowest (82 bu/ acre). The average yield of the 30-inch twin row and 15-inch row systems were similar (86 bu/acre) (Figure 2).


Figure 2. Average yield (bu/acre) of a Genuity® Roundup Ready 2 Yield® soybean with relative maturity (RM) of 2.4 to row spacing configurations for trial conducted in 2012.

Figure 3 shows the 7.5-inch row configuration had a 12 per cent and 7 per cent average yield increase over the 30-inch row and both the 15-inch row and the 30-inch twin rows, respectively. These values equate to 10 and 6 bu/acre yield reductions for the 30- inch and both the 15-inch and the 30-inch rows, respectively.


Figure 3. Average yield loss of a Genuity® Roundup Ready 2 Yield® soybean with relative maturity (RM) of 2.4 planted in three row spacing configurations compared to drilled (7.5-inch) single row for trial conducted in 2012.

Canopy closure in the 7.5-inch drilled soybeans may have occurred earlier than in the 30-inch row configuration. Testing in Iowa showed a 4.5 bu/acre yield advantage for 15-inch over 30-inch row spacing1. Testing in Nebraska showed a 2.2 bu/acre yield advantage for 20-inch over the 30-inch row spacing2.

Due to earlier canopy closure, narrow rows can have a larger yield advantage when the soybean planting date is delayed into June. Canopy closure is needed by the start of pod set (R3) for maximum pod formation and seed filling2.

In general, narrow rows decrease the time to canopy closure, which can help leaves intercept more light throughout the season. Additionally, the time to canopy closure can have a significant impact on soil moisture loss, ability to control emerging weeds, and especially on crop growth rate.

The overall minimal yield difference across row spacing configurations might be due to several factors. The unusual drought in 2012 combined with disease pressure, late rain, and high temperatures during the critical growth stages may have negatively impacted soybean yields. Additionally, previous factors might have negated the benefits of the different configuration systems that were implemented in this study.

In a similar study conducted in 2011, drilled soybeans produced the highest yields. On average, the 7.5-inch drilled soybeans had a 20 -35 per cent increase in yield over the 15, 30, 36-inch and the twin row configurations. The 30-inch row yielded less than the drilled soybeans but relatively similar yields to 15- and-36-inch row and the twin row configurations.

Summary Comments

  • The 7.5-inch row drilled soybeans produced the highest average yield (92 bu/acre) while the 30-inch row produced the lowest yield (82 bu/acre).
  • Average yield from 15-inch and twin rows were similar.
  • The average yield differences between row space configurations in 2012 might be due in part to the unfavorable environmental conditions of drought and unusually high temperatures during critical growth stages.
  • Always consider proper soybean product selection, seedling population, row spacing, and fungicide application strategies to help reduce stress and help optimize soybean yield potential.
  • The extended period of high temperatures and low rainfall during the growing season contributed to the below average yields recorded for soybean in 2012.

Additional testing is needed to better understand the effects of row spacing under different field environmental conditions.

Figure 4. Soybean V3 (L) and V4 (R) growth stages.

Sources: 1Pedersen, P. 2008. Row spacing is important to maximize your yield. Soybean Production Fact Sheet 3/12/2008. Iowa State University Extension. http://extension.agron.iastate.edu (10/18/12).
2Elmore, R.W. et al. 1990. Narrow-row soybeans. University of Nebraska-Lincoln Cooperative Extension. NebGuide G90-963 issued November 1990.
3Monsanto National Research Summary. 2009. Interaction of plant population, row spacing and variety selection on soybean yield. Monsanto Technology Development.
4Plant Health Initiative. 2009. Soybean row spacing. http://www.planthealth.info (10/10/12).

March 2014

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