On research plots in Stoneville, Miss., scientists now have some preliminary data many soybean farmers have been anxious to receive. In a side-by-side comparative study of standard, 40-inch, single-row soybeans versus twin-row, two 10-inch rows (based on a 40-inch center), conducted this past growing season, researchers determined that soybeans in twin rows produced more pods and higher yields than those in single rows.
Trey Koger, soybean agronomist at the Agricultural Research Service's Crop Genetics and Production Research Unit, said he and Dan Poston, Mississippi State University Extension soybean specialist, were not necessarily surprised at the results.
“Twin rows produced, on average, five more pods per plants. Even though that may not sound significant, it is. That adds up to more than half a million more pods an acre in the twin-row system versus the number of pods per acre in the single-row system,” Koger said.
Koger and Poston believe the difference in pod production and soybean yields between the two systems is based on light interception. Since plants in the twin-row system were separated into two rows rather than one in the study, they intercepted almost twice as much light as plants in the single-row system.
In recent years, farming equipment companies have been increasingly marketing twin-row planters over the conventional, single-row planters.
Koger said some equipment representatives estimate that the twin-row planter will provide as much as 2 percent to 10 percent increases in soybean yields. Koger's study showed similar results: Soybean yields totaled 80 bushels per acre in the twin-row system compared to 73 bushels per acre in the single-row system, marking an 8.5 percent increase in yields in the twin-row system.
While some farmers have seen such an advantage, a scientific, independent comparative study had not been conducted until now.
Koger said an even more important discovery in the study was learning that it may not be necessary to increase seed rates in using the twin-row planting approach to increase yields when compared to single-row planting.
“Now that finding did surprise us somewhat. We thought we would see a difference in the seeding rate but we didn't,” he said. “In order to compare seeding rates while keeping the plant population the same across twin-row and single-row systems, we planted four, five or six seeds per foot of row in the twin-row system and eight, 10 or 12 seeds per foot of row in the single-row system. This allowed us to compare seeding rates across both systems. Soybean yields ranged from 76 to 78 bushels per acre across all seeding rates in both the twin-row and single-row system.“
The fact that seeding rates did not affect yield is noteworthy Koger said, because it means farmers can increase yields without having to increase seed purchases, up to a point.
Companies offering twin-row planters have recommended that farmers should increase seeding rates by 20 percent to see optimal yield differences between the two planting systems. “Based on results from the first year of our study, it indicates that increasing the seeding rate was not necessary in order to increase yields, but additional research is needed to fully address the seeding rate issue,” he said.
Based on questions from growers, Koger plans on comparing the twin-row and single-row systems to soybeans planted in a more conventional 15- to 20-inch row spacing versus soybeans drilled in 8-inch rows all at the same plant population and at 20 percent higher seeding rates than what is currently recommended. This study will be conducted under both irrigated and non-irrigated settings.
“There is a lot of interest in this from soybean growers. Visitors at our field day over the summer were particularly curious about our study. Some returned to visit the plots,” he said.
George Ray Walker, a soybean and corn farmer in Leland, Miss., has used a twin-row planter for about five years. He has been “very pleased” with the system and plans to stay with it in the future.
Walker turned to twin-row management because of plowing restrictions on his farmland. He is not certain how much credit for his high yields can go toward the twin-row system and how much can be credited for the dual-crop rotation method.
He did estimate that while soybean yields have been slightly higher on some parts of his soil, yields have been significantly higher — as much as seven or eight bushels — on heavier soil areas. He attributes increases to the twin-row planter.
“Farmers are really taking a closer look at this based mostly on the higher yield increases,” he said.