Soybeans are adaptable, branching out when you give them room, but how much elbow space does a soybean plant need? Iowa farmers have been growing soybeans in widths from 6 to 40 inches with varying results, but is there an optimum?

For Mark Licht, Iowa State University field agronomist, and Andy Lenssen, ISU soybean systems agronomist, that row-width question offers some interesting answers. Looking at the difference between 15-inch and 30-inch rows with four seeding rates at three Iowa locations from 2004 to 2006, in work done by ISU researchers, for example, they found some noteworthy results. Seed weight and plant height were largely unaffected by row spacing, but yield was 4 bushels higher per acre in narrow rows. There was more production of seed per unit area in the narrow-row setting.

Interestingly, seeding rates didn’t make much of a difference in the results. The narrower rows produced higher seed yields across a range of planting rates.

Another ISU study compared four row widths — 5 inches, 10 inches, 20 inches and 40 inches. In that study, maturity date, plant height and lodging were relatively unaffected across the range of widths. Seed yields were highest in the narrower 5- and 10-inch-row plots. The 20-inch plot was a middle-ground performer, and the 40-inch rows produced the least.

Licht and Lenssen also looked at data from Indiana and New York and found similar results. Soybeans like narrower rows, and across a range of studies, consistently outperform wide-row plantings.

One worry for farmers who stay with wide rows is white mold. However, new technology in the form of a new fungicide — Aproach from DuPont — could alleviate that concern.

While narrow rows were the closest determining factor for rising yield, work has also been done at ISU regarding soybean plant populations. And while you often hear about 150,000 plants per acre and higher as the goal for an emerged stand, turns
out the most important number may be a little lower.

ISU research shows that a uniform final stand higher than 100,000 ppa didn’t increase yield, but if your stand is lower than 100,000 ppa, you would see significantly lower yields.

So how much do you have to plant? Take a look at your stand counts versus planting rates. For example, if you planted at 160,000 ppa and got a final stand of 130,000, that’s an 18.75% reduction. To hit that optimum 100,000 ppa, given that loss, you’d need to plant 125,000 plants per acre.

If you’re looking at a new soybean planter for 2014, thinking narrow and fine-tuning plant populations could put more soybean profit on your bottom line.