Herding cattle. Counting fish. Taking an animal's temperature. Applying pesticides.

When it comes to drones, "your imagination can go pretty wild in terms of what would be possible", said Roger Johnson, president of the US National Farmers Union.

This month, the US Federal Aviation Administration issued the first permit for agricultural use of unmanned aerial vehicles. Steven Edgar, president and CEO of ADAVSO, said his Idaho-based business will use a lightweight, fixed-wing drone to survey fields of crops.

Drone technology, already used in other countries, can make farmers more efficient by helping them locate problem spots in vast fields or ranchlands. Increased efficiency could mean lower costs for consumers and less impact on the environment if farmers used fewer chemicals because drones showed them exactly where to spray.

The Association for Unmanned Vehicle Systems International, a trade group, said agriculture could account for 80 percent of all commercial drone use, once government regulations allow it. That could be a while. The Federal Aviation Administration has been working for years on rules that would balance the desire for commercial flights of small drones with the need to prevent collisions involving manned aircraft.

Here are four ways drones could affect the food supply:

Scouting farms

The first agriculture drones are looking at massive fields of crops to scout out where crops are too wet, too dry, too diseased or too infested with pests. They can help farmers count plants or measure their height. Farmers can now use satellite technology, but it's slower and less detailed than images from low-flying drone.

Alabama farmer Don Glenn said he would buy a drone or use a service that provides drone surveillance on his farm of corn, wheat, soybeans and canola. It's hard to survey corn fields when they are 2.4 meters to 3 meters tall, he said.

Drones can carry different tools, including high-resolution cameras, infrared sensors and thermal sensors. Ground-penetrating radar could even measure soil conditions.

Applying chemicals

Once the land is surveyed, farmers could use that data to narrow the areas that need treatment. If a plot of farmland is infested with weeds, for example, a farmer could spray a small amount of herbicide just in that area, instead of an entire field, to kill them. Farmers hope that they eventually could use drones to do the spraying.

Kevin Price of the Iowa-based drone company RoboFlight Systems said that kind of precision would put farmers at a huge advantage, helping them reduce the costs of chemicals.

Finding fish

A University of Maryland project is developing drone technology to monitor fish in the Chesapeake Bay. Matt Scassero, the project director, said the idea is that a laser-based sensor mounted on a drone would allow scientists to see through the water and measure the size of a school of fish.

Some drones can land on water, making it possible to measure water quality, as well.

Revealing secrets

There are downsides for farmers. Filmmaker Mark Devries used an unmanned vehicle to fly over large commercial hog operations and film them.

R.J. Karney of the American Farm Bureau Federation says there is a "major concern" about those kinds of films and intends to work with the Obama administration and Congress to address it. He said such films are not only a privacy violation, but can put farmers at a competitive disadvantage.