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. Not only does lettuce need to be fertilised and weeded, but also "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 Stanford-trained engineers, Jorge Heraud and Lee Redden. Their diligent robotic labourer, pulled behind a tractor, takes 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. If this sounds bonkers, 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 image data fast enough to work with 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 active in agribusiness. The launch of a fully operational, ruggedised 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.
