Combined Penetrometer and Standing Wave Ratio Probe to Measure Compactness and Moisture Content of Soils

Compactness and moisture content are important and mutually influential soil parameters that affect plant growth, nutrient absorption, and nutrient transportation.To simultaneously measure these two parameters, we developed a combined penetrometer standing wave ratio (PSWR) probe; acceleration measurement was facilitated to eliminate the error caused by varying penetration speeds.The performance of the instrument was analyzed and verified through laboratory and field measurements.The cone-index measurements from an SC-900 sensor and the moisture content calculated by the drying method and a TDR sensor were used to evaluate the performance.The results prove that acceleration compensations can improve the accuracy of cone-index measurements.Further, the sensitive range of the PSWR probe was the area a 10 cm diameter.The linear-fitting coefficient of output voltage and volumetric moisture content exceeded 0.96, and the output was stable; therefore, the moisture content measurements using the PSWR probe were validated.Furthermore, the accuracy and stability of measurements using the PSWR probe and a TDR sensor were similar.The field-measurement results agreed with the results from the drying method, and satisfied the practical implementation requirements.Conclusively, the validated efficiency and the cost-effective stainless-steel structure of the probe render it suitable for practical applications.