An improved root crop harvester having a narrow and compact processing chassis adapted to simply and easily receive header assemblies of differing capacities. The header assemblies include a transverse roll conveyor for gathering roots received from the digger wheels into a stream for discharge through a central opening in the transverse conveyor to a fore-and-aft extending roll conveyor carried by the processing chassis. The fore-and-aft roll conveyor is inclined upwardly from front to rear to increase the scrubbing and tumbling action and is also provided with a reversing roll section at its rearward end to discharge the roots to the side. The fore-and-aft conveyor is also sloped across its width at its rearward end to aid in discharging roots transversely to the roll conveyor length. The conveyors on the processing chassis are carried between the support wheels to reduce side drafts, minimize wheel slippage in wet field conditions and improve transport maneuverability.