Farmers from across the nation gathered in Washington this month for their annual trek to seek action on the most important matters in American agriculture.

But this time, a new issue emerged: growing unease about how the largest seed companies are gathering vast amount of data from sensors on tractors, combines and other farm equipment. The sensors measure soil conditions, seeding rates, crop yields and many other variables.

Seed companies want to harness the data to help farmers grow more food with the same amount of land. But some farmers worry that the information could be hacked or exploited by corporations or government agencies. And they are serving notice that Congress might need to become involved in yet another debate over electronic security and privacy.