WSB study: Deer don’t always damage soybean yields

Soybean farmers tend to think white-tailed deer (Odocoileus virginianus) are major culprits behind lost yields. A new study conducted in Mississippi, however, points to other detrimental factors related to the vegetation and soil surrounding crop fields.

“Where deer were browsing, they did affect the height of the soybean plant, but there was no difference in the yield,” said Bronson Strickland, lead author on the paper published in the March issue of the Wildlife Society Bulletin.

The study addressed soybean producers’ interest in keeping deer from ruining their crop and aimed to assess the severity of the damage. From 2012 to 2013, researchers examined five small fields surrounded by forests supporting stable deer populations. The biologists protected parts of all sites with deer-proof fencing. Throughout each year, they measured plant height and percent of plants damaged in the unfenced regions. At the end of the growing season, they compared plant height and yield between the fenced and unfenced areas.

“Deer did not destroy a soybean crop or minimize the yield under the conditions tested, typical for the southeastern United States,” Strickland, associate extension professor of wildlife ecology and management at Mississippi State University, said.

This could be because deer browsing triggers compensatory growth, he said. The plants produce more stems in response to herbivory, allowing them to preserve yield.

Strickland also found that plots by field boundaries had lower yields than plots in the middle, regardless of whether deer could access them. According to these results, characteristics at the field margin could be an important influence on yield.

“There’s more competition with adjacent trees for water, sunlight and nutrients,” he explained. “There’s soil compaction from machinery where farmers stop and turn.”

Browsing at the edge or center of a field doesn’t have to mean reduced yield, Strickland said. If deer density is so high that the animals truly are causing a problem, he suggests spraying deer repellant on the soybeans or establishing fences in the secluded corners deer are likely to enter from.

“Protect soybean plants until they become established,” Strickland said. “Once that plant has developed its root system and gets to be 12 to 18 inches high, that plant can typically handle deer browsing. It’ll keep growing.”

Strickland’s finding that the deer had no significant negative impact on soybeans aligns with previous research in Delaware that discovered that light browsing could actually boost yield by promoting branching in the plant.

In about a month, Strickland and his colleagues will use drones to scout for destroyed plants in soybean fields in the state to better determine the role of deer and other causes in the damage.