The Department of Agricultural and Biological Engineering at the University of Illinois at Urbana-Champaign, divides agricultural robots into three generations. The first gen is comprised of basic ones that can collect data, while the second-gen bots are capable of harvesting, seeding, spraying and cultivating. Finally, the third and most advanced generation is comprised of autonomous robots capable of caring for plants without (or with minimal) human intervention. As you can see below, American farms already use machines from across three generations, though most of the ones that fall under the third are still in development.

CURRENT AND UPCOMING ROBOTS ON AMERICAN FARMS

Some of the most well-known farming robots out there are shake-and-catch machines for oranges and other citruses, which literally shake trees side to side and up and down to harvest fruits. Obviously, they can collect fruits more quickly and efficiently than humans can, allowing farmers to plant more trees and increase their output. According to the University of Florida, a particular type of shake-and-catch machine being used to harvest oranges in the state can fill 100 boxes with fruits per hour per crew member. There are apple harvesters currently in development as well, but they're much harder to design, since apples get bruised and damaged easily.

Earlier this year, a tree nursery in Florida hired a fleet of robots called HV100 (or "Harvey"), designed by Boston firm Harvest Automation. These Wall-E-like robots autonomously space out saplings as they grow bigger and pack them tightly when it's time to sell them.

Just like Harvey, Blue River Technology's Lettuce Bot is an automaton, which, as you could guess, can make sure rows upon rows of lettuce are growing perfectly. In 2012, a Lettuce Bot prototype was tested at "the Salad Bowl of the World," Salinas Valley in California, where it crawled along rows of green veggies like a strict teacher doing rounds during an exam. The robot analyzes each plant, comparing it against more than a million images of lettuce in its database, to determine if it's a weed (or an errant lettuce growing too close to another) that needs to be eliminated. Its creators plan to tweak Lettuce Bot in the future, so it can be used on other crops.

A Minnesota company, on the other hand, spent more than 14 years developing a tractor that drives itself. It doesn't use GPS so it can't navigate streets like Google's autonomous car can -- instead, it responds to ground-based transponders planted around the perimeter of your land. The self-driving vehicle finds its way around the field based on the map it creates after you take it around for the first time. To be sure that it doesn't accidentally go on a rampage, its creators designed it to shut down if a transponder determines that it's straying from its path. It's also equipped with radar in order to avoid trees and other objects. The company believes that the tractor has potential to be used for mining and groundskeeping vehicles. There are also many monitoring robots, like one San Diego company's Crop Load estimator, used to estimate the amount of fruits or vegetables that a farmer can expect.

It's not just fruit and veggie farmers that are going high-tech, though: Many American dairy farmers have started using robotic milkers. They actually just set up these milkers on their farm, allowing cows to line up for milking whenever they want. Aside from being able to milk the animals, though, the machines can also monitor how much each cow has eaten, the number of steps she's taken per day and, of course, the amount and quality of milk being produced.

AERIAL DRONES FOR FARMS OF THE FUTURE

While we always hear about drones being developed for the military and law enforcement, at least one person in the industry believes it has bigger potential in agriculture. Speaking to Wired, Chris Mailey of the drone-promotion organization AUVSI, says farming has fewer hurdles to overcome and, at the same time, farmers are motivated by the potential rewards of early adoption.

While the Federal Aviation Administration hasn't approved drones for farming yet, it's already begun testing one, (which can not only monitor crop conditions, but also test soil quality) in North Dakota. Some farmers are already using drones, though, such as this 17-year-old Redditor from Southwest Kansas, who flies a drone from Kansas company AgEagle over his family's land to take infrared images of their crops and determine their health. His family then uses data gathered from those infrared images to adjust fertilizer distribution as needed. Most aerial drones for farming have the same function, giving farmers an aerial view of their crops so they can save water, chemicals and fertilizer.

THE FUTURE OF ROBOTIC FARMING

Farm robots are not without fault -- big machines, in particular, damage the soil and make it prone to erosion. The Mitchells and their neighbors' machines, for instance, have weakened the soil in the area and made it prone to erosion . Still, there's no going back now, and you'll likely see a variety of machines performing different functions on big farms across the globe. The US, in particular, seeks to develop better robots for the country's farmers: The Department of Agriculture's National Institute of Food and Agriculture is currently spending the $4.5 million funding it set aside in 2013 to fund various agrobot projects. Long story short: It's just the beginning for robot-powered agriculture.

Update (10/02/14): Clay Mitchell reached out to Engadget and wants to clarify that he personally doesn't use tillage machines, which cause soil erosion. He says he even uses other techniques like cover cropping to combat the issue, making his soil "more protected than many natural systems."

"There are a lot of tradeoffs in farming and many controversial ideas about how to farm," he wrote in his email. "But where there is a tradeoff, I go for protecting the soil every time." Mitchell also adds that he often volunteers his time talking about farming methods that prevent soil erosion, and various farming agencies from around the globe have asked him to spread those methods in their countries.