Homogeneity of crop establishment, which directly depends on physical conditions within the seedbed, is very important for crop yield. We did a field experiment to test the abilities of various sensors to characterise seedbed physical conditions and the possibility of continuously modifying the intensity of soil tillage with the objective of producing a uniform seedbed. The experiment was done on a silt soil with 19% clay and 74% silt in northern France. We created two initial soil structures (with and without clods >10 cm) and controlled water content (field capacity or less). A special cultivator was developed with a continuous-output GPS and a microwave ground-based radar sensor; it also carried a laser profile meter for soil surface characterisation, a capacitance probe for monitoring soil water content, and a load cell for measuring soil mechanical resistance. Each sensor was able to detect differences in soil physical conditions at the field scale. Because of the simultaneous effect of soil water content and soil structure on the geophysical parameters obtained with the sensors, it was not possible to obtain a continuous characterisation of the soil’s bulk density, water content, clod-size distribution, or surface roughness (although the use of two radar angles of incidence might allow better assessment of soil surface roughness). For tillage control, seedbed conditions depended on initial soil conditions (water content and degree of compaction) and soil tillage tool characteristics (working depth and speed of rotation). Working depth and speed of rotation had opposite effects on the size of clods at the seedbed surface; within the seedbed, they could reduce initial soil variability. Seeding rate could be controlled by the same sensors if they were put in front of the seeder. Results of the experiment are relevant to spatial parameterisation of existing soil models.