FIG. 1 is a front view of our agricultural tractor; FIG. 2 is a rear view thereof; FIG. 3 is a right side view thereof; FIG. 4 is a left side view thereof; FIG. 5 is a top plan view thereof; FIG. 6 is a bottom view thereof; FIG. 7 is a front view of our agricultural tractor according to a second embodiment of our ornamental design; FIG. 8 is a rear view of the second embodiment; FIG. 9 is a right side view of the second embodiment; FIG. 10 is a left side view of the second embodiment; FIG. 11 is a top plan view of the second embodiment; and, FIG. 12 is a bottom view of the second embodiment.