An instrumented shank was designed and built to measure mechanical impedance of soil at multiple depths over the entire top 18 in. of soil profile while moving through the soil. GPS-based equipment was developed and tested for controlling the tillage depth “on-the-go” to match soil physical parameters. An electro-hydraulic actuator and proportional directional control valves were used to move the gage wheels on a four-row subsoiler-bedder upward or downward to control the tillage depth. Also, tests were conducted for two years on a coastal plain soil to compare variable-depth tillage with the constant-depth tillage and no-till system in terms of effects on soil parameters and crop responses.

It was possible to determine the optimum tillage depth using a cone penetrometer, electrical conductivity meter or the instrumented shank. Also, it is possible to control the tillage depth “on-the-go” to match soil physical parameters. Variation in the predicted tillage depths to eliminate the hardpan layer ranged from 10 to 18 in. Based on penetrometer data, approximately 75% of the test area required tillage operations shallower than the recommended tillage depth for coastal plain soils. There was a strong positive correlation between EC readings and seed cotton yield. Also, the predicted tillage depths were inversely correlated to the soil electrical conductivity. Soil texture was found to override the effects of deep tillage operation. For sections of the field with high clay contents and depth to B-horizon less than 13 in., there were no differences in yield between variable depth tillage, no-till, and conventional tillage operations. In the sandier part of the field with depth to clay layer more than 13 in., there was a significant difference in yield between no-till and the other two tillage treatments. The energy savings of 42.8% and fuel saving of 28.4% were achieved by variable-depth tillage as compared to uniform-depth tillage.