Abstract: A system for maintaining the depth of a planter (or tiller) at a soil depth of optimal moisture content is provided, in which a prior art soil resistivity sensor is improved by including a negative electrode immediately behind the prior art positive electrode as the planter and electrodes extend into the ground during tractor travel over the field. The prior art positive probe is shaped to form a compact ribbon of soil therebeneath that extends from the positive to the new negative probe. This compact ribbon provides a reliable and consistent path for measuring soil resistivity at a soil zone of least electrical resistance, thereby preventing other pathways between the positive electrode and grounded parts of the planter or tiller from undesirably entering the detection system in lieu of the desired pathway of measurement.

Abstract: A soil contacting implement and depth gauging wheel at a predetermined vertical distance from the implement are provided for attachment to a tractor. Upward or downward movement of the wheel on the soil causes a deviation from the predetermined vertical displacement thereby triggering an adjustment to the downward force on the implement so as to reestablish the predetermined displacement. The magnitude of the predetermined displacement manually may be altered. In addition, the downward force of the wheel manually is adjustable without altering the magnitude of the predetermined displacement.