By Scout Nelson
Researchers at South Dakota State University are developing biodegradable hydrogel beads that may help crops receive nitrogen naturally. The technology takes inspiration from Mexican corn and soybean root nodules, where bacteria work in low oxygen environments to fix nitrogen.
SDSU researchers Srinivas Janaswamy and Senthil Subramanian lead the study, which explores how hydrogel beads can protect nitrogen-protecting bacteria and support their activity. The research is published in Plant and Soil and focuses on creating a small environment similar to natural root nodules.
Nitrogen is essential for plant growth, but most plants cannot use nitrogen gas directly from the air. Certain bacteria can convert nitrogen into forms plants can use. However, the nitrogenase enzyme that supports this process is highly sensitive to oxygen.
Scientists observe that some Mexican corn varieties use a gel like material around aerial roots to create conditions that support nitrogen fixing bacteria. Soybeans also use root nodules to provide bacteria with a suitable low oxygen environment.
The SDSU team uses alginate, a biodegradable material made from seaweed, to create similar conditions. The researchers test calcium, strontium, zinc, nickel, copper, and aluminum. They also test two nitrogen-fixing bacteria, Azospirillum brasilense and Herbaspirillum seropedicae.
Calcium beads perform best. They maintain low oxygen levels, capture more than 70% of the bacteria added to them, and help keep the bacteria alive longer. The bacteria inside calcium beads also show nitrogenase activity similar to bacteria grown under ideal laboratory conditions.
“One of the biggest challenges in using free-living nitrogen-fixing bacteria in agriculture is protecting the nitrogenase enzyme from oxygen while still allowing the microbes to remain active," Subramanian said.
The team also tests glucose as an energy source. Glucose increases nitrogenase activity in Herbaspirillum seropedicae but reduces activity in Azospirillum brasilense, showing that bacterial responses can differ.
The beads gradually biodegrade in soil over 120 days. This makes the technology potentially useful for sustainable farming.
“Nature already provides examples of microorganisms fixing nitrogen efficiently when they live in the right microenvironment, "Janaswamy said. "Our research demonstrates that biodegradable hydrogels can recreate these conditions, supporting biological nitrogen fixation by maintaining the environment required for the nitrogenase enzyme to remain active.
Future studies will test the beads under real soil and plant growing conditions. The technology could eventually help supply nitrogen to crops such as corn and wheat while reducing dependence on synthetic fertilizers.
Photo Credit: south-dakota-state-university
Categories: South Dakota, Crops, Sustainable Agriculture