By GOSIA WOZNIACKA and TERENCE CHEA -
On a windy morning in California's Salinas Valley, a tractor pulled a wheeled, metal contraption over rows of budding iceberg lettuce plants. Engineers from Silicon Valley tinkered with the software on a laptop to ensure the machine was eliminating the right leafy buds.
The engineers were testing the Lettuce Bot, a machine that can "thin" a field of lettuce in the time it takes about 20 workers to do the job by hand.
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