WESTERN PRODUCER — Soybeans are considered self-pollinating plants that rely little on pollinators.
Even so, bees contribute to their pollination and yield potential.
Researchers at North Carolina State University have discovered that soybean crops planted close to pollinator habitat produce larger soybeans than those planted farther from pollinator regions. Pollinator habitat refers to areas managed to promote nectar, pollen and nesting resources for beneficial arthropods and pollinating insects.
“I have been working on documenting the impacts of adding pollinator habitat into agricultural areas as a conservation tool for bee populations for several years,” said Hannah Levenson, postdoctoral research scholar in entomology and plant pathology.
“We had investigated several aspects of this in bee populations but were interested in better understanding the impacts of added habitat on nearby crops. There is quite a bit of previous literature investigating this interaction in pollinator-dependent crops. We chose to investigate soybeans as they are grown almost everywhere and have a great potential to be impacted by pollinators and vice versa.”
Levenson stated in the report that soybeans are one of the top crops grown worldwide with an estimated 305 million tonnes produced between 2020 and 2021 globally. According to Soy Canada, Canada produced almost 6.3 million tonnes in 2021.
Levenson said while many growers consider soybeans to be pollinator-independent, research has documented increased yields from bee pollination.
Levenson’s study focused on the specific value of bee habitat nurtured close to soybean fields.
“Our study is unique in that we were investigating the impacts of added (pollinator) habitat for the first time,” she said. “We documented only those bees actively visiting soybean flowers (and so likely contributing to pollination) and verified that bees were collecting resources while in soybean fields with pollen identification. We were very excited to find that the addition of habitat alone still resulted in larger soybean seeds.”
The research team collected samples from eight of the 18 research stations across North Carolina. The stations regularly plant soybeans and are located in different ecoregions across the state.
The habitat-sampling plots ranged in size from 0.2 acres to 0.75 acres, while the sampling area for each soybean field was 1.3 acres on average.
In 2019, they sampled bee pollinators at three sites within each of the eight stations. Sampling methods were both visual and netting surveys.
“On average, the adjacent soybean fields were 112.3 metres away from the pollinator habitats, and the negative control fields were on average 964.7 metres away,” she said.
A wildflower mix was maintained for the habitat plots.
To obtain an accurate profile of the bees, the researchers surveyed bee communities in the soybean fields and the pollinator habitats at each of the eight research stations. They assessed the overall abundance of bees and documented which bee species were present at each location. They also collected samples of individual bees to confirm their identifications.
“The main bee groups we found in the pollinator habitat were bumblebees, long-horned bees, and sweat bees,” she said. “The main bee groups found in the soybean fields (both the adjacent fields and the negative control fields) were honeybees, bumblebees, leafcutter bees, and carpenter bees. However, the bee communities in the adjacent soybean fields were more similar to the bee communities in the habitat area than in the negative control fields because they had more long-horned and sweat bees.”
She added that the main bee species in their region in southeastern U.S. is likely to be different from the expected bee species in other regions of North America.
The research team collected pollen samples from three of the most common bee species, which allowed them to document the plants the bees were visiting.
They determined that all the bees found in any of the soybean fields were actively visiting soybean flowers. However, the bees in the soybean fields located at a distance from pollinator habitats were often leaving the soybean fields to visit flowers outside the range of the study area. Bees in soybean fields adjacent to pollinator habitats were less likely to leave the study area.
The report stated that the researchers found soybean pollen on all specimens collected in the soybean fields suggesting that bees were collecting resources (pollen, nectar, or both). Specimens collected in the adjacent crop sites had significantly more habitat pollen types while some specimens from the negative control crop sites had significantly more environmental pollen types.
“From the survey, we found that the bee communities in the pollinator habitats were completely distinct from the bee communities in the distant soybean fields,” said Levenson.
“The bee communities in the soybean fields adjacent to pollinator habitats were something of a mixture, including elements of both groups. The habitat-adjacent fields were fairly similar to the distant soybean fields but had bee communities that were clearly influenced by the nearby pollinator habitat.”
At harvest, the researchers collected 30 soybean plants from each of the study fields. They counted the number of seeds per pod, the number of seeds per plant and the weight of the seeds.
“We found that the number of seeds was similar for fields near pollinator habitat and fields that were far away,” she said.
“However, plants in fields that were adjacent to pollinator habitat produced seeds that were 6.5 percent heavier than the seeds from plants in distant fields.”
Levenson expects similar crops such as fababeans could also benefit from the influence of pollinator habitat.
“There are many benefits from planting pollinator habitat in agricultural areas, and our paper provides evidence for even more benefits,” she said.
“Overall, these benefits can include reduced management inputs (since sections of land no longer need to be maintained as regularly if planted with pollinator habitat), increased soil retention, increased water quality, support for pollinator populations, increased bee visitation to nearby crops, and increased crop yield. The pollinator habitats we sampled were often planted in unusable or difficult areas of the farm. Planting this pollinator habitat can be a win-win-win for the land, beneficial organisms, and the landowner.”
The immediate benefit to the farmer is a yield with a substantial improvement in the size of the soybeans and therefore weight gain.
“Given that soybean farmers sell their crop by weight, it could make a meaningful difference in a grower’s profit margin,” said David Tarpy, professor and extension specialist of applied ecology at North Carolina State University.
Levenson said regions outside the U.S. southwest have different cropping systems, so it is not known how these findings would apply to those areas.
The research was published in the journal Agriculture, Ecosystems & Environment.
