Different sources for similar ‘horses’: John Deere’s former 3000/3010 was a green Renault Ceres, its current 5010 tractors are made by Agritalia, while the all-new 5020 line comes from its own German factory. The reality is that the 5020s complement, rather than supersede, the 5010s, and will be sold alongside them. Martin Rickatson takes a drive