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Variable−depth tillage has the potential for economic and environmental benefits to modern crop production. Varying tillage depth according to local soil conditions prevents the waste of energy and preserves soil ecology. A prototype instrumentation system was developed based on a conventional implement for deep tillage. It was equipped with two load cells and two sets of strain gauges for sensing the load applied to the implement during tillage. Two linear pressure distribution models (full and redundant) were used to describe the change of soil mechanical resistance with depth. These models were then used to compare estimates of soil mechanical resistance applied to the point of the deep−tillage implement based on predicted and measured values. Field evaluation was conducted to illustrate the system’s performance in two experimental sites. In both cases, instrument predictions corresponded with soil profile measurements obtained using a standard cone penetrometer. The developed system may become a part of variable−depth tillage equipment after an algorithm for a closed−loop tillage depth control is developed.