Development of a motorized digital cone penetrometer

Quantification and management of variability in soil strength, or soil compaction, is an important issue in countries such as Korea and Japan where typical field sizes are small, but tractor mounted on-the-go sensors that have been developed in USA and European countries are not practical. Therefore, hand-operated digital penetrometers have been widely used in Asian countries, but maintaining standard penetration rate and angle would be difficult. In this study, a motorized digital cone penetrometer that could penetrate up to 50 cm was developed. The penetrometer was small and light device enough to be transported manually to allow movement on wet-paddy fields and narrow greenhouse inter-rows. The penetrometer included 3 cone tips to reduce data collection time, an electrical motor to push the cone tips into the soil, an encoder to measure penetration depth, a frame and rubber wheels, and a central processing unit to control the motor and log sensor data and differential global poisoning system (DGPS) position. The prototype sensor could detect vertical cone index (CI) variations and peaks similar to a hand-operated commercial unit, but they were less erroneous, represented actual soil strength levels better, and reduced nugget variances significantly, due to a stable penetration rate and angle.