On a bright, hot day this June in Arizona, a vehicle the size of a Golden Retriever, designed and constructed at the University of Illinois, rolls on miniature tank treads between two rows of young plants. A group of researchers, policy-makers, and farmers have gathered to see the early fruits of an unusual hybridization in modern agriculture: a crop of semi-autonomous robots designed to monitor the growth of sorghum and other crops, born of a cross between plant biology and engineering.