A method of mapping the depth of a trench (3) opened in a soil surface (7) of a field by an agricultural row unit (10) attached to a planter is provided. The method involves receiving a trench depth signal from a depth sensor (150； 1226) associated with the row unit (10). A measured trench depth value is determined based upon said trench depth signal and a calibration curve. A GPS position of the planter is reported by a GPS receiver (550). The trench depth value and the GPS position of the planter are recorded and time-stamped. An image correlated to the measured depth on a map at a map location corresponding to the GPS position of the planter at the time of the depth measurement is displayed.
