Cotton is the world’s most widely grown and economically important nonfood crop. In the United States alone, farmers grow cotton on 12 million to 14.5 million acres, and produce a yearly harvest worth nearly US$25 billion.
Before cotton’s fluffy bolls emerge, the plant produces large white flowers, similar to those of the hibiscus. These flowers attract a wide range of insects, including bees, flies, butterflies and beetles, which visit the flowers to collect nectar and pollen as food and act as pollinators, moving pollen between flowers.
Plants make seeds after male-produced pollen grains and female plant ovaries are brought together. Some plants are self-pollinating, but others need pollinators to help the process along. While cotton can produce marketable, fiber-filled fruits without the help of pollinating insects, pollinators significantly increase the weight of cotton bolls. Larger bolls produce greater yields and higher profits for growers.
Pollinators are under threat worldwide, and their plight threatens both farmer yield and the pollination of natural vegetation. Populations of honeybees, which are widely used commercially to pollinate crops, have fallen in at least 18 European countries, as well as in the United States. Wild pollinators – including 20,000 bee species worldwide – may be suffering a similar fate.
Using the tools of landscape genetics and ecology, the Jha lab is looking for ways to restore and maintain pollinators in agricultural landscapes, which would offer an opportunity to increase crop yields and profits while also benefiting the environment. In a recent study, we showed that cotton farmers in Texas may be able to both increase their yields and help pollinators thrive by increasing the amount of natural land cover surrounding cotton fields.
Pollinating cotton in South Texas
To see whether we could develop strategies that would benefit both pollinators and farmers, we worked with landowners and local cotton growers in South Texas. Using geographic information systems (GIS), we chose cotton study sites that offered varying quality of resources to local pollinators – that is, nesting areas and food supplies nearby. Then we measured the abundance and diversity of pollinator species at each site. In total, we found that 52 species of insects visited cotton flowers at the sites to feed on either nectar or pollen.
Lastly, we estimated how well each of our sites was being pollinated. Using some simple techniques, we compared the size of bolls produced in three treatments.
In the first treatment, we measured the size of bolls produced when pollinators were excluded from visiting. This “no pollination” treatment simulated a potential worst-case scenario in which pollinators were entirely absent.
For the second treatment, we allowed pollinators to visit as they normally would. This “typical pollination” treatment measured how well the pollinators at each site were doing if we just left them alone.
Lastly, we created a treatment where we, as researchers, acted as “super-pollinators,” moving lots of pollen between flowers with the aid of tremendous patience and very small tweezers. In this “perfect pollination” treatment, we simulated a best-case scenario in which pollinators did a perfect job of moving pollen between flowers. In this way, we were able to measure how well typical pollinators at each site were doing as compared to a worst-case scenario (“no pollination”) and a best-case scenario (“perfect pollination”).
More plants nearby produce better pollination
Our results showed that sites with patches of natural area nearby – for example, oak woodlands or natural shrublands – had the most abundant and diverse pollinators. Sites that were close even to small amounts of natural forest or shrubland had both more individual pollinators and more species of pollinators visiting cotton flowers. We believe this relationship reflects the fact that natural areas contain nesting and food resources important to pollinator health.
Further, we found flowers that received “perfect pollination” produced bolls that were on average 18 percent heavier than those that received “typical pollination” treatment. This means that pollinators could provide greater benefits to farmers if they have more support. In fact, at sites where pollinators were more abundant and diverse, the “typical pollination” treatment bolls were much closer in size to the “perfect pollination” bolls. At sites that lacked diverse and abundant pollinators, the “typical pollination” bolls were much closer in size to the “no pollination” treatment.
Expanding our finding that supporting pollinators increased cotton yields by 18 percent to the entire South Texas region, we calculated farmers using this strategy could earn an average of $108 more per acre. This translates into an increase of more than $1 million yearly for growers in the region.
Bringing back pollinators
Our results suggest that even small patches of natural habitat in or around farmed land can help to establish and maintain diverse and abundant pollinator communities, which in turn boosts cotton crop yield.
While it may take a few years for natural areas, such as oak woodlands or natural shrubland, to mature after land managers create them on agricultural land, there are also ways to increase pollinator habitat more quickly. Growers can plant rows of wildflowers between rows of crops or on the edges of crop fields to provide food for pollinators. Farmers can also introduce flowering crops, such as sunflowers, okra, watermelon or musk melon, into their crop rotations.
Another strategy is to set aside small fields to go fallow for a year or two, allowing flowers to reestablish in their own time. Lastly, growers can reduce tillage in fields, which would preserve important nesting habitat for many of the pollinator species that visit cotton flowers.
People who are not farmers can help by growing wildflowers in their yards and gardens, especially varieties that bloom at different times during the year. For suggestions specific to your region, see the Xerces’ Society for Invertebrate Conservation.
With these small steps, growers can produce big profits with relatively little input. And the benefits have the potential to spill over into other crops that need pollinators, such as watermelons, blueberries and almonds. They would also benefit natural and urban areas, such as parks and playgrounds – and maybe even your own backyard.