A soil characteristic sensor is mounted on a soil engaging element of a planting machine. It can be mounted, for instance, on an element that engages the soil before a trench is opened, or after a trench is opened, but before it is closed. It can be mounted on an element that engages the soil in a region of the soil trench, but after the trench is closed. It can be mounted on a scraping element that scrapes a disc, and it can be mounted on wedges or other items that run through the soil, and are carried by shanks.