A mobile turf instrument apparatus (100, 300, 400, 500) for measuring a turf infill profile, which comprises: a frame (21, 54, 404, 504) supported for movement over a turf surface; a measurement apparatus carried on the frame for measuring the vertical distance between an upper profile position and a lower profile position, wherein the measurement apparatus comprises a probe assembly (27, 27') for measuring a turf infill profile of a synthetic turf surface, the probe assembly comprising: at least one probe (28, 420, 520) that is configured to extend down through the turf infill profile until a lowermost tip of the at least one probe contacts a backing material comprising a lower boundary of the turf infill profile; a turf surface contact assembly (30A, 408, 508), which is vertically movable relative to the at least one probe while the at least one probe is being moved downwardly into the turf infill profile, wherein the turf surface contact assembly is vertically movable relative to the lowermost tip of the at least one probe and has a contact area with the turf surface that is large enough to retain the turf surface contact assembly resting atop an upper boundary of the turf infill profile when the lowermost tip of the at least one probe has contacted the lower boundary of the turf infill profile, and a sensor (38, 405, 505) for reading the distance between the upper and lower boundaries of the turf infill profile at a sampled location in the turf surface; a computer having a central processing unit, a memory coupled to the central processing unit and an electronic interface coupled between the instrument assembly and the memory for transferring the measured vertical distance; a variable rate top dresser (4, 4'), wherein the variable rate top dresser outputs a particulate application rate; in which the computer is configured to vary the particulate application rate so as to cause infill particulate material to be added from the variable rate top dresser to low spots in the turf surface as detected by the sensor. a frame (21, 54, 404, 504) supported for movement over a turf surface; a measurement apparatus carried on the frame for measuring the vertical distance between an upper profile position and a lower profile position, wherein the measurement apparatus comprises a probe assembly (27, 27') for measuring a turf infill profile of a synthetic turf surface, the probe assembly comprising: at least one probe (28, 420, 520) that is configured to extend down through the turf infill profile until a lowermost tip of the at least one probe contacts a backing material comprising a lower boundary of the turf infill profile; a turf surface contact assembly (30A, 408, 508), which is vertically movable relative to the at least one probe while the at least one probe is being moved downwardly into the turf infill profile, wherein the turf surface contact assembly is vertically movable relative to the lowermost tip of the at least one probe and has a contact area with the turf surface that is large enough to retain the turf surface contact assembly resting atop an upper boundary of the turf infill profile when the lowermost tip of the at least one probe has contacted the lower boundary of the turf infill profile, and a sensor (38, 405, 505) for reading the distance between the upper and lower boundaries of the turf infill profile at a sampled location in the turf surface; at least one probe (28, 420, 520) that is configured to extend down through the turf infill profile until a lowermost tip of the at least one probe contacts a backing material comprising a lower boundary of the turf infill profile; a turf surface contact assembly (30A, 408, 508), which is vertically movable relative to the at least one probe while the at least one probe is being moved downwardly into the turf infill profile, wherein the turf surface contact assembly is vertically movable relative to the lowermost tip of the at least one probe and has a contact area with the turf surface that is large enough to retain the turf surface contact assembly resting atop an upper boundary of the turf infill profile when the lowermost tip of the at least one probe has contacted the lower boundary of the turf infill profile, and a sensor (38, 405, 505) for reading the distance between the upper and lower boundaries of the turf infill profile at a sampled location in the turf surface; a computer having a central processing unit, a memory coupled to the central processing unit and an electronic interface coupled between the instrument assembly and the memory for transferring the measured vertical distance; a variable rate top dresser (4, 4'), wherein the variable rate top dresser outputs a particulate application rate; in which the computer is configured to vary the particulate application rate so as to cause infill particulate material to be added from the variable rate top dresser to low spots in the turf surface as detected by the sensor.