On-the-Go Mapping of Soil Mechanical Resistance Using a Linear Depth Effect Model

Abstract

An instrumented blade sensor was developed to map soil mechanical resistance as well as its change with depth. The sensor has become a part of the Integrated Soil Physical Properties Mapping System (ISPPMS), which also includes an optical reflectance and a capacitor-based sensor implemented to determine spatial variability in soil organic mater and water content, respectively. The instrumented blade of the ISPPMS was validated in laboratory conditions by applying known loads. It was also tested in the field by comparing sensor-based estimates with measurements produced using a standard vertical cone penetrometer and another on-the-go sensor, the Soil Strength Profile Sensor (SSPS), consisting of five prismatic-tip horizontal penetrometers located at fixed depths. The comparison resulted in reasonable linear relationships between corresponding parameters determined using the three different methods. The coefficient of determination (r2) for average soil mechanical resistance was 0.32 and 0.57 when ISPPMS-based estimates were compared with the standard cone penetrometer and the alternative on-the-go sensor (SSPS), respectively. Depth gradients of soil mechanical resistance obtained using cone penetrometer and ISPPMS methods were correlated with r2 = 0.33. Observed differences in estimated parameters were due in part to the difficulties with obtaining data representing the same depths and in part to differences in sensor geometry and operating conditions, particularly when comparing the on-the-go sensors to the cone penetrometer. Based on its operation during Missouri field mapping, the instrumented blade proved to be a rugged and inexpensive sensor suitable for studying the spatial variability of the physical state of soils in the upper 30 cm of the profile.