Field comparison of two prototype soil strength profile sensors

Soil compaction that is induced by tillage and traction is an ongoing concern in crop production, and also has environmental consequences. Although cone penetrometers provide standardized compaction measurements, the pointwise data collected makes it difficult to obtain enough data to represent within-field variability. Moreover, penetrometer data exhibit considerable variability even at a single location, requiring several measurements to obtain representative readings. For more efficient data collection, on-the-go compaction sensors that obtain data at multiple depths are being developed by several research groups. The objective of this research was to evaluate and compare the field performance of two on-the-go compaction sensors. Tests were conducted at two central Missouri field sites where soil types ranged from sandy loam to clay. The soil strength profile sensor (SSPS) measured compaction to a 50-cm depth on 10-cm intervals. The soil compaction profile sensor (SCPS) also used five sensing elements and obtained data to 40.6 cm on a 7.6-cm interval. Cone penetrometer measurements of compaction were obtained at intervals along each transect for comparison. Data were compared between the two on-the-go sensors and were also related to penetrometer and soil property data. The repeatability of SCPS data was somewhat better than that of SSPS data. Data from the two sensors were linearly related, with similar regression equations for each individual site and for both sites combined. The agreement between SCPS and SSPS data (r² = 0.56 over all sites and depths) was much better than between sensor and penetrometer data (r² = 0.19-0.20). Maps of SCPS and SSPS data for a 13.5-ha field site showed very similar patterns. Maps of penetrometer data were also similar to those of on-the-go sensor data, but showed fewer spatial details. Variation in soil strength appeared to be primarily related to variations in soil physical properties (e.g., texture, water content). Due to the similarity between SCPS and SSPS data, we conclude that measurements obtained with the two on-the-go soil sensors were affected similarly by soil strength variations within the study sites. Side-by-side comparison of the on-the-go sensors provided a convenient approach to validate sensor performance. The study also provided information to improve on-the-go sensor design and to relate sensor data to other measures of soil compaction.