Kubota M100GX Operator's Manual page 74

52 OPERATING THE TRACTOR
C Field mode
In plowing operation, the automatic shift-up/down is carried out within a predetermined range (factory-set for 2 shifts),
responding to the field condition, soil condition and other factors. When lifting the attachment using 3 pt, the automatic shift-
down is made for easier turning.
With implement that require PTO rotation, automatic shift-up/shift-down occurs repeatedly. This is because the system is
sensitive to the load from the plow or other towed implements. As a result, the PTO speed is kept nearly constant, improving
the accuracy of work.
A The tractor has been factory-set for the automatic range (2 shifts) discussed above. This gearshift range can be
modified to meet your applications. (For details, refer to "Changing the Auto-Mode settings" in this section.)
A The Auto-Mode does not function if the clutch is disengaged or halfway or in turning (over the bi-speed turning angle)
and if shuttle lever is in reverse position.
A The Auto-Mode functions when the engine rpm is above the middle speed.