An agricultural planter having sensors for measuring multiple soil properties adjusts planting depth and seeding rate in real time based on the measured soil properties. An optical module is carried by the planter for collecting soil reflectance data. A pair of soil contact blades protrude from or are embedded in the optical module for collecting soil EC data and soil moisture data. A switching circuit or phase lock loop allows the same soil contact blades to feed signals to both a soil EC signal conditioning circuit and a soil moisture signal conditioning circuit. The soil moisture data can be used to calibrate the soil EC data and the soil reflectance data to compensate for effects of changing soil moisture conditions across a field. The sensor module can be positioned behind a seed tube and used as a seed firmer, or incorporated into a seed tube guard.