Narrow soybean rows could produce less weeds, more yield

COLUMBIA, Mo. – Narrower row width is one key to reducing weeds in soybean, says University of Missouri Extension weed scientist Kevin Bradley.

In previous research, Bradley reported improved late-season weed control (density and/or biomass) in 64% of case studies (72 out of 113 site-years) in soybean.

Narrow rows allow soybean leaves to shade the ground and prevent weeds from germinating. The canopy keeps late-emerging, herbicide-resistant weeds such as waterhemp from getting a foothold.

When integrated with a traditional herbicide strategy, this practice could provide more effective weed management, he says. Narrow rows will help to suppress weed numbers in soybean but not completely eradicate weeds. Because soybeans are weak early-season competitors, you must still start with a clean seedbed and use effective pre-emergence residual herbicides. The narrow canopy then takes over to choke out subsequent flushes.

More yield

While most Missouri soybean growers choose either 15- or 30-inch row spacing, 15 inches or narrower may have advantages besides weed management.

University of Missouri Extension soybean farming system specialist Andre Reis has also found that 15-inch rows can increase yields by 6-10 bushels per acre compared to 30-inch rows. Reis heads MU’s Variety Testing Program.

His research shows that row spacing is the second-strongest predictor of yield, following planting date. Overall, his research shows that 15-inch row spacing yields better than 30-inch rows in most parts of Missouri, except in the southeastern region, where row spacing had no effect.

In addition to improving yields and facilitating weed management, narrow rows can reduce soil erosion, Reis says. With wider rows, it takes longer for the soybean canopy to close over exposed soil between rows, making the soil more prone to erosion.

However, narrow rows can have disadvantages. The switch to narrower rows can pose additional challenges, such as the implementation of surface irrigation. Additionally, in wet springs, narrow rows can prolong soil moisture after rainfall, making the crop more susceptible to disease.

Follow Reis’ Soybean Growth Monitoring Tool, which simulates soybean development and yield across different regions of Missouri.

Photo

Planting soybean in rows 15 inches apart or less may help suppress weeds, boost yield and limit yields. MU Extension file photo.