Abstract
1. Roughness of the field surface, soil hardness and sinkage of tractor wheels were continuously measured while tilling, and the influence of them on low-frequency fluctuations of the tilling torque and the tilling depth were investigated.
2. When the automatic control system was not applied and the height of the three-point hitch wass fixed, the tilling torque and the tilling depth were fluctuated mainly by the roughness of the field surface if the soil hardness was relatively large and uniform. While if the soil hardness was small, they were fluctuated mainly by the sinkage of tractor wheels.
3. When the gauge wheels were applied, the tilling torque and the tilling depth were fluctuated by the sinkage of tractor wheels and gauge wheels if the soil hardness was small.
4. In case of tillage under the automatic control of the travelling speed and the tilling depth, low-frequency fluctuations of the torque and the depth were small. And their correlations to the field roughness and the soil hardness were also small. However, the tilling torque fluctuated transiently when the rotary tiller was lifted and lowered.
