As she pushed a button to bring the eight-propeller drone back to the ground, dandelion fluff swirling in the air, U.S. Sen. Joni Ernst joked that she was ready for a job as a commercial fertilizer applicator.

“Do you have a contract you need to fulfill?” she asked Michael Ott, chief executive officer and founder of Rantizo, an agricultural drone company based in Iowa City. (…)