Twin-row soybeans can provide the same yield advantage as 30-inch soybeans without significant changes to wide-row equipment, according Trey Koger, agronomist at the USDA/ARS, Stoneville, Miss.
“We can plant the twin-row pattern on an 80-inch bed or a 40-inch bed, giving us a narrow-row spacing of somewhere around 30 inches, and we can still use our existing production system set up on 38- or 40-inch beds. The twin-row system is a narrow-row spacing in a wide-row system,” Koger said.
Koger spoke about his research on twin-row soybeans versus wide-row soybeans during the Conservation Systems Cotton and Rice Conference, in Tunica, Miss.
Two varieties were selected for the study, both early-season Group 4 varieties. One was short stature and bushy, Asgrow 4201. The other was a tall, slender upright, Asgrow 4403.
For the single-row, 40-inch system, researchers planted 8, 10 and 12 seeds per foot of row. In the twin-row pattern, they planted at 4, 5 and 6 seeds per foot of row. “We did that to compare the twin-row system with the single-row system at the same seeding rates.”
The experiment was planted on a heavy clay soil at the experiment station. Beds were 80 inches wide and accommodated two, twin-row plantings or two single-row plantings. They sprayed the entire study with a strobilurin fungicide at R-3 to R-4. The twin-row study was planted with a Great Plains twin-row drill. The single-row study was planted with a John Deere vacuum planter.
“We did not see any plant population differences between the twin-row system and the single-row system. This told us that the twin-row drill did just as good a job as the planter in getting a stand. This also meant that since there was no difference in plant population, we could compare the yield.”
Yield data across all three plant populations indicated the twin-row pattern out-yielded the single wide-row pattern by 8 percent, or 7 bushels.
“The twin-row pattern yielded more, but there was not a seeding rate response. This is good information because there is some data out there that suggests that you increase your seeding rate by 20 percent with a twin-row pattern.”
Twin-row plants canopied about 10 days earlier than single-row plants, according to Koger. “That might save you a herbicide application, but more importantly, we intercepted more light in the twin-row system. The increased light interception allowed the plants in the twin-row system to produce five more pods per plant.
“That doesn't sound like a lot, but if you extrapolate that out on an acre basis, it's about a half-million more pods per acre. That's what's accounting for the increased yield.”
Early findings also indicate the twin-row system won't out-yield a 30-inch system if drainage is the same across both systems. “But we're going to conduct some more research on that this coming season.”
Studies by USDA/ARS in Stoneville, Miss., indicate that as row spacing increases above 30-inches, soybean yields tend to go down. Conversely, yields trend higher as you move from a wide row to a 30-inch spacing. However, studies indicate that you don't gain appreciable yield by going narrower than 30 inches.