Continuous measurement of horizontal soil mechanical resistance at multiple soil depths with a multiple blade system

Soil compaction limits root penetration below the plowing depth, reduces yields, and makes plants more susceptible to drought stress. Applying uniform-depth tillage over the entire field to manage the soil compaction may be either too shallow or too deep and it can be costly. Variable-depth or site-specific tillage technology optimizes soil physical properties only where the tillage is needed by applying tillage at the required depth. Therefore, there is a need for a technology to determine the tillage depth based on soil mechanical strength at different depths of soil. Since soil cone penetrometers require a stop-and-go operation that can be time consuming and costly, on-the-go measurement methods of soil mechanical strength have been investigated by some researchers. A measuring system with multiple instrumented shanks was designed and built to measure mechanical impedance of soil at different depths over the entire top 40 cm of the soil profile while moving through the soil. This system allows shanks for the simultaneous measurement of soil mechanical resistance at four depths, while moving through the field. The design allowed 10cm of measurement depth per instrumented shank. Each instrumented shank consisted of an extended octagonal load cells. Each shank was calibrated in the lab by applying known forces and measuring output voltages. DT800 data logger (dataTaker Co., UK) was used for data collection. Soil strength data was collected at 150Hz. The instrumented measurement system was calibrated against cone penetrometer readings at same depth intervals by collecting intensive geo-referenced penetrometer data from a predetermined path and then running instrumented system with multiple shanks in the same path. The penetrometer data was averaged over 10cm intervals and compared to the average force measurements from each instrumented shank of measurement system. There was a correlation with R2=0.77 (the least correlation coefficient) at 0-10cm depth and R2=0.83 (the most correlation coefficient) at 30-40cm depth between soil cone penetrometer data and instrumented measurement system values. Results showed that soil moisture content had a significant effect on horizontal soil mechanical strength and cone index data. Changes of working depth had a significant effect on horizontal soil mechanical strength and cone index data. Ground speed had not significant effect on soil mechanical strength measured data.