[en] Knowledge of local soil strength variation may permit variation of tillage parameters to produce a more optimal soil structure for root growth and plant development. Soil strength mapping can provide another layer of information in precision agriculture. The aim of this research is to develop a sensor able to measure on-line the local soil strength variations. This sensor is designed as follows: a thin blade penetrates the soil to a specific depth while the machine is moving, a beam transfers the soil-blade forces to a transducer fixed on the machine. The transducer measures then the horizontal and vertical forces and the moment. This paper describes a field experiment performed in a 2 ha field of silt soil (Hesbaye, Belgium). The first objective of this research is to establish a map of soil strength variability of the field. For this purpose, the sensor is pulled through the soil in parallel traverses at 5 m separation by a tractor equiped with a DGPS receiver. The second objective of the experiment is to study relation between measured forces and several measured soil physical parameters. Ten homogeneous plots where identified on the sensor track in order to cover as completely as possible the diversity of soil physical conditions encountered. On the median line of each of those plots, 10 Cone Index penetrometry profiles were measured with a mobile automated penetrometer recorder, soil water content was measured in 5 points, ans soil samples were taken in the center of the plot to determine the following parameters: cohesion and internal friction angle, simple compression resistance, Atterberg's limits, granulometry and pF curves. This experiment allowed the first identification of different soil strength areas in the field investigated.