Plant Health Initiative

Soybean Row Spacing

Yield of soybeans grown in northern latitudes are largely limited by the short growing season. In general, production practices that encourage the greatest use of the sun’s heat and light provides the best opportunity to maximize yields. One such practice is narrow row spacing (less than 30 inches).

Minnesota agronomists have reported that reducing row spacing from 30" to 10" can result in a 3-8% increase in yield. This yield benefit is generally even greater in the northern part of the state where the short growing season is an even larger factor in soybean yield capacity. Similarly, late-planted or soybeans planted in a no-tillage system often show large yield increases in narrow rows compared to wide rows due to earlier canopy closure. Recent multi-year studies in Iowa have shown an average 4.5 bu./acre yield increase using 15-inch row spacing, compared to 30-inch row spacing.

"A View From Below". Photo of a  30-inch soybean canopy (left) compared to a 15-inch canopy taken from the soil in mid-July. Photo credit: Chris Boerboom, University of Wisconsin

The main benefits of narrow row spacing is early canopy closure

Early canopy closure increases crop growth rate, dry matter accumulation, and seed yield. Canopy closure of 15-inch rows will often happen 15 days earlier than 30-inch rows. This is critical since canopy closure is needed by the start of pod set (R3). Often soybeans grown in 30-inch rows fail to achieve canopy closure by this critical yield-determining growth stage. Other benefits of narrow row planting and early canopy closure are:

• better weed control. Early canopy closure shades out competing weed seedlings.
• reduced soil moisture loss
• easier and more efficient harvesting than harvesting soybeans in wide rows. Combine efficiency is increased because a more even distribution of plants makes them easier to cut and feed into the combine. Harvest losses are reduced because there are no cultivator ridges to interfere with cutting height.

Some obstacles to narrow row spacing

• Lack of equipment to plant in narrow rows. Split-row planter technology may overcome this obstacle by providing optimal row spacing for both corn and soybeans. Split-row planters have additional row units between traditional 30-inch row units that can be raised or lowered depending on the crop. Although split-row technology is more expensive, the return on investment is relatively high considering an the yield advantage with narrow row planting.
• Failure to achieve a uniform stand  or yield benefit in the past. There are cases when narrow rows yield the same as wide rows, and this is often due to the presence of diseases like brown stem rot or soybean cyst nematode, which negate the yield benefit of narrow row planting when susceptible varieties are planted.

Sources

Soybean Planting Considerations The Bulletin, University of Illinois

Row Spacing in Soybean (pdf format) - Iowa State University

Minnesota Soybean Field Book (pdf format) - University of Minnesota

Re-Thinking Soybean Row Widths - Ontario Department of Agriculture

Optimum Soybean Plant Populations in Iowa (pdf format) - Iowa State University