Design, Fabrication and Evaluation of a Tractor-Mounted Soil Cone Penetrometer with Multiple Probes

Soil compaction is a major problem in many parts of the world. The determination of soil compaction profiles requires fast sampling systems to keep pace with the change in soil moisture condition over time. Soil cone penetrometers are commonly used for this purpose. A tractor-mounted soil cone penetrometer was designed and fabricated with multiple probes and the ability to determine cone index values in crop rows. The multiple probe penetrometer, composed of mechanical, hydraulic and electrical components, can evaluate soil strength conditions to a depth of 45 cm. The mechanical section comprised a frame to support the other sections of the unit and was mounted to a tractor using three-point hitches. Hydraulic power was used to force the probes into the soil. Using a data logger, data was collected from the load cells and depth sensors and sent to a computer to develop the cone index curve. To evaluate the penetrometer, the soil cone index was measured under two soil conditions (stubbly and plowed) and two soil moisture levels (before irrigation and after irrigation). The penetrometer was then tested and evaluated in comparison with a hand-pushed penetrometer under the same test conditions ata 15 depths. The coefficient of correlation between the hand-pushed and tractor-mounted penetrometers for stubbly and plowed soil was determined as R2 = 0.98 and R2 = 0.98 (before irrigation) and R2 = 0.96 and R2 = 0.97 (after irrigation), respectively. The t-test revealed that the cone index was not significant for the tractor-mounted and hand-pushed penetrometers at 5% confidence levels. Thus, the tractor-mounted penetrometer can be used for soil strength measurement with high confidence.