Forage harvesters may be trailed, tractor mounted or self-propelled with either a pick-up attachment or flail cutting unit. Power take-off driven trailed and mounted forage harvesters cut or pick up the green material, then chop it into short lengths and blow it into a trailer in one operation. Most trailed forage harvesters have a pick-up cylinder varying in width from 1.5 to 3 m and an off-set drawbar. Some are double chop machines with a flywheel chopping mechanism and others are precision chop harvesters with a cylinder chopper or cutterhead.
Figure 15.1 Forage harvesting with a 308 kW (414 hp) self-propelled harvester. (Claas)
Precision chop, self-propelled harvesters with hydrostatic transmission, mainly used by agricultural contractors, have the capacity to harvest from 50 to 120 ha (125 to 300 acres)'or more of grass in a day. They are very expensive. Most have four-wheel drive, hydrostatic transmission and, depending on size, an engine in the range of 150-525 kW (200-700 hp) or more.
The driver in the forage harvester cab shown in Plate 15.3 controls harvesting operations with a joystick and a group of switches by the side of the seat. The joystick controls the forward speed, reverses the feed roll to clear blockages, raises and lowers the pick-up cylinder, rotates the delivery spout and alters the angle of the chute extension. An emergency stop button on top of the joystick instantly cuts off the drive to the front end if there is a blockage or other problem. The bank of switches near the seat controls almost every other function from changing gear ratio and engaging the main harvesting clutch to activating the metal detector and operating the rear trailer hitch. Panels of indicator lights on the windscreen corner post monitor engine functions, harvester operation, forward speed, fuel level, four-wheel drive engagement, etc.
Self-propelled forage harvesters can be used with various types of header including a pickup cylinder, a" range of maize headers cutting from'4 to 10 rows at a time and a whole crop silage header similar to that on a combine harvester for harvesting legumes and cereal crops while they are still green. Some models can also be used as the power unit for a very wide front-mounted mower.
Plate 15.2 A 230 kW (310 hp) diesel engine provides the power for this self-propelled forage harvester with a 3 m wide pick-up cylinder. (John Deere)
Plate 15.3 Electronic switches on the right-hand side of the seat enable the driver to control the harvesting operation from the cab. (John Deere)
Plate 15 4 An off-set precision chop forage harvester with a high sided trailer towed behind. The box on the crop delivery chute contains the electric motor which rotates the spout and alters the chute extension angle. (Claas)