LETTUCE is California’s main vegetable crop. The state grew $1.6 billion-worth of the leafy plant in 2010 and accounts for more than 70% of all lettuce grown in America—itself the world’s second-biggest exporter of the stuff. It is a fiddly business. As well as having to be fertilised and weeded, lettuce must also be “thinned” so that good plants do not grow too close to each other, inhibiting growth. Much of this is still done by hand. Labourers, who tend to be paid per acre, not per hour, have little incentive to pay close attention to what they pull from the ground, often leading to unnecessary waste.
Enter Lettuce Bot, the brainchild of two Stanford-trained engineers, Jorge Heraud and Lee Redden. Their diligent robotic labourer, pulled behind a tractor, starts by taking pictures of passing plants. Computer-vision algorithms devised by Mr Redden compare these to a database of more than a million images, taken from different angles against different backdrops of soil and other plants, that he and Mr Heraud have amassed from their visits to lettuce farms. A simple shield blocks out the Californian sun to prevent odd shading from confounding the software.
When a plant is identified as a weed—or as a lettuce head that is growing too close to another one—a nozzle at the back of the unit squirts out a concentrated dose of fertiliser. This sounds bonkers, but it turns out that fertiliser can be as deadly as a pesticide, which is why farmers usually sprinkle it at a safe distance of 10-15cm from the plants to be nourished, so as to dilute its effect. So the robot not only kills weeds and excess heads, but feeds the remaining crops at the same time.
The battery-powered system crunches the images fast enough to work at 98% accuracy while chugging along at a bit less than 2kph. In September Blue River Technology, a start-up founded by Mr Heraud and Mr Redden, raised $3m from Khosla Ventures, a venture-capital firm. The launch of a commercial version of the robot is planned for next year. Mr Heraud is coy about Lettuce Bot’s cost, but says it will be competitive with manual labour.
Its creators are also working on a machine capable of excising weeds mechanically using a rotating blade. Indeed, the robot was originally conceived as an automated lawnmower for parks and other public places but legal issues—think spinning metal blades in areas frequented by children—prompted Mr Heraud and Mr Redden to turn to agricultural users instead. That would make it a boon to California’s organic farmers, who eschew the potent, weed-killing fertiliser. Next in Mr Heraud’s and Mr Redden’s sights is corn (maize), America’s biggest crop. Teaching the robot to deal with plants like tomatoes, where distinguishing weeds from the crop can be hard even for humans, will take longer.
Lettuce Bot is just one of many robots intended to automate aspects of agriculture and horticulture that are still highly labour-intensive, even in the rich world. The Vineland Research and Innovation Centre in Ontario is working on one robot to plant tulip bulbs and replant seedlings, another to harvest, trim and package mushrooms and a third to package potted plants. And the Harvest Vehicle HV-100, otherwise known as Harvey, built by Harvest Automation, a firm based in Massachusetts, is designed to move potted shrubs and trees around in plant nurseries. Where these machines lead, other green-fingered robots may follow.