Row width is one of the management practices most often considered by growers as potentially important to increased soybean yields and profits. Extensive research studies conducted over many locations and years have compared drilled narrow rows vs. 30-inch rows in soybeans, and have generally shown a significant yield advantage for drilled narrow rows.
In recent years, however, drilled soybeans have fallen out of favor in many areas, likely due to inferior seed placement and singulation capabilities of drills versus planters, and the cost of planting additional seeds. As a result, soybeans planted in 15-inch rows have gained in popularity as a way to capture some of the yield benefit of drilled narrow rows while using a planter instead of a drill. Research on soybeans in 15-inch rows is less extensive, having been conducted mostly within the last 10 to 15 years as this row spacing has gained popularity.
Recent Row Spacing Research
A review of soybean row spacing studies published within the past 10 years generally confirms previous results comparing 30-inch rows and drilled narrow rows. In five studies, drilled soybeans outyielded 30-inch row soybeans by an average of 4.1 bushels per acre (bu/acre). Six studies that compared 30-inch rows and 15-inch rows found similar results, with 15-inch rows holding a 3.6 bu/acre yield advantage. Yields were similar between 15-inch row and drilled narrow-row soybeans in these studies.
Because most of these studies used higher seeding rates with narrower rows, increased seed costs partially offset the narrow-row yield benefit. Higher seeding rates with narrower rows have been a common practice, particularly with drilled soybean; however, not all research supports this practice.
A study conducted in 2008-2009 (Cox and Cherney, 2011) found no row spacing by seeding rate interaction for soybeans planted in 7.5-inch, 15-inch, and 30-inch spacings. Recent research conducted in Iowa had similar results, indicating that narrow-row systems do not necessarily require a greater harvest stand to maximize yield (Pedersen, 2008).
Historically, less accurate seed placement made higher seeding rates necessary with drills; however, improved seed placement with newer precision drills has reduced this need. In light of these findings, seed cost may not be a requisite consideration for row spacing decisions.
As noted, recent research studies have shown a 3 to 4 bu/acre yield advantage for soybeans planted in drilled narrow rows or 15-inch rows compared to 30-inch rows. In spite of this clear advantage, row spacing preferences vary greatly across North America, and 30-inch row soybeans are common and even gaining in many areas. This demonstrates that many different considerations beyond simply yield potential can affect the best practices for each individual grower. Factors such as equipment costs, workload management and disease management all play an important role. When those issues are accounted for, narrow-row planting is not necessarily the best economic choice for all operations. Because of this complexity, no one-size-fits-all answer should be applied. Rather, each grower should carefully consider the costs, risks and benefits of soybean row spacing options in their operation.
The full article outlining the agronomic findings of DuPont Pioneer can be read by clicking here.