ARS | Publication request: On-the-go mapping of soil mechanical resistance assumed to change linearly with depth

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 6, 2008
Publication Date: N/A

Interpretive Summary: Precision agriculture aims to minimize costs and environmental damage caused by agricultural activities, and to maximize crop yield and profitability, all based on information collected at within-field locations. Soil strength, an indication of compaction, is a factor that can vary considerably within fields and can also greatly affect crop yields. Because of this, farmers need a quick and inexpensive way to measure compaction, such as could be provided by an on-the-go sensor. This research compares two new on-the-go sensors that can take measurements continuously at multiple depths while traveling across a field. In field tests we found that the on-the-go sensors performed well and gave comparable results. We also compared our sensors to the cone penetrometer, a device commonly used to measure compaction. Both sensors showed similar trends in compaction to those shown by the penetrometer. However, sensor measurements were easier to obtain and resulted in maps with more detail than the penetrometer measurements. Both sensors show promise as potential tools for improved compaction measurement. The results of this study will be useful to scientists and engineers seeking to improve on-the-go sensor design and to develop efficient test methods for evaluating sensor performance.

Technical 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 and a capacitor-based sensor. The instrumented blade of the ISPPMS was validated in laboratory conditions by applying known loads. It was also tested in the field by comparing recorded data with measurements produced using a standard vertical cone penetrometer and with another on-the-go sensor, the Soil Strength Profile Sensor (SSPS), consisting of five prismatic-tip horizontal penetrometers operated at different 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 compared with the standard cone penetrometer and the alternative on-the-go sensor (SSPS), respectively. The differences observed were due in part to the difficulties with obtaining data representing the same depths and due to differences in sensor geometry and operating conditions, particularly when comparing the on-the-go sensors to the cone penetrometer. Depth gradients of soil mechanical resistance obtained using cone penetrometer and ISPPMS methods were correlated with R2 = 0.33. The instrumented blade proved to be a rugged, rigid, and inexpensive sensor suitable for studying the spatial variability of the physical state of soils.