A tractor-mounted soil cone penetrometer for mapping spatial variability of soil strength

A tractor-mounted, automated soil cone penetrometer was designed, constructed and tested for the purpose of measuring cone index throughout the entire soil profile. We propose the use of cone penetrometer profile to assist in mapping 3-dimensional spatial variability of soil strength. The apparatus consisted of a mechanical frame, an assemblage of control hardware and a laptop computer with the controlling software. A double-acting hydraulic jack with 80 cm stroke was mounted on the frame to push the cone into soil. A load cell and a digital caliper were used for measuring pushing force and depth, respectively. A DC motor was mounted on a power screw to activate a directional control valve and. The data acquisition module and an external global positioning system (GPS) were used to assist in real-time measuring, displaying, and recording the tractor position and soil penetration resistance. Soil strength maps of five layers with 10 cm increment and mean soil moisture content were plotted. Results showed that in the first 10 cm layer, soil compaction was related to the soil moisture content but it was not occurred about other layers. Finally combining maps of soil strength made an effective soil profile in order to tillage with different depth.