Row width trends in soybeans
Other Row Spacing Considerations
Foliar Fungicide and Insecticide Applications
The need for fungicide and/or insecticide applications may also impact row spacing decisions. When an application is made during vegetative growth, plants are generally able to compensate for damage caused by the sprayer wheels with little reduction in yield. For applications made following the R1 growth stage, which would include most foliar fungicide and insecticide applications, wheel damaged areas will have lower yield. A research study conducted in Delaware and Virginia found significant yield reductions due to sprayer wheel damage in R4 soybeans planted in 7.5-inch and 15-inch row spacings, whereas soybeans planted in 30-inch and wider row spacings did not sustain any sprayer wheel damage (Holshouser and Taylor, 2008). Actual yield loss due to wheel traffic will vary according to boom width (Table 2).
The growing prevalence of weed populations resistant to glyphosate has made weed management more challenging in some areas; consequently, it is becoming increasingly necessary to consider the impact of cropping system factors such as row spacing on weed growth. In general, weed growth will be reduced in soybeans planted in narrower row spacings and earlier shading by the soybean canopy will help suppress the emergence of new weeds. The extent of this effect will vary by weed species and weed emergence timing relative to the crop (Hock et al., 2006).
Planting and Harvest Efficiency
Crop residue can be an important consideration when planting soybeans, particularly in the northern Corn Belt where residue management is more of a challenge. Some growers in high residue systems prefer wider rows because there is more room to deposit residue between the rows, which helps prevent residue interference with planting and emergence.
Narrow-row soybeans offer some harvestability advantages over soybeans in 30-inch rows. The lowest pods will tend to be higher in narrow-row soybeans, potentially reducing harvest losses. The more even distribution of plants in narrow rows also allows plants to feed into the combine head more smoothly, although some growers have found that harvesting 30-inch row soybeans at an angle can help improve harvestability.
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.