Once a week for seven months, AnnElise and Caleb Brostrom and Madison Arndt went out in their backyards with a tub of animal fat, looking for spindly buckthorn plants.

The three teens were trying to see if the animal fat might serve as a natural alternative to harsh chemicals commonly used to beat back the invasive shrubs, which steal light, food and moisture from native plants. The results? They found that 12 of 15 shrubs tested showed no regrowth after 30 weeks.

The three presented their research to a panel of judges recently at the 4-H Science of Agriculture Challenge. Now in its second year, the challenge is designed to inspire the next generation of agricultural leaders.

The goal is to research and develop real-world solutions to modern agricultural problems, like the stubborn spread of buckthorn. The participants, from sixth-graders to college freshmen, worked for months with mentors and agricultural experts.

This week, 14 teams of 4-H'ers from all over the state gathered in St. Paul to present their work. Projects included programming drones to protect livestock from predators and using iron-infused sand and wood chips to filter out nitrogen in drain tiles near the Minnesota River.

A 4-H group from Dakota County that developed a warming pouch for vaccines went home with the top prize, a $1,000 scholarship. The ­second- and third-place teams developed GPS livestock ear tags and solutions for food waste.

The Anoka County 4-H team used a visual aid during its presentation on killing buckthorn trees with animal fat with a visual aid.

"I was really impressed with the innovation of these teams," said Joshua Rice, the program's coordinator. "They really became experts."

According to the Bureau of Labor Statistics, there are more than 25,000 new jobs for management and business in agriculture annually and more than 14,600 jobs in agriculture and science engineering. But only 5 percent of U.S. students get their undergraduate degree in science and engineering — a statistic that Rice hopes the challenge might change.

"So many young people think agriculture is only animals and crops and farming," said Anna Brekke, a recent high school graduate and member of the Scott County team that developed a water filtration model. "I think this challenge helps us look beyond that."

In the fall, Brekke plans to study sustainable systems management at the U of M.

Of the teenagers who participated last year, Rice said, nearly 90 percent wanted to pursue a career in agriculture.

AnnElise and Caleb's mom, Theresa Brostrom, said she enjoyed watching the teens engage. "What kid goes out every week for 30 weeks to smear fat on a tree stump?" she said. "...Kids who realize that young people are capable of a good idea that can make a difference."

Mara Klecker • 612-673-4753