Roundabout

This is fairly difficult. The way I did it was to go through the field directly to the north of the starting point first, then quickly switched over to the field to the east of that, then the field to the east of THAT, then to the field to the south of THAT, then to the field to the west of THAT.

At this point you'll have cleared all the northern fields, and will want to go to the fields south of the starting point.

Go to the southeast from the field you're in to get to the next field. Quickly plow through as much of it as possible, and boost through the other two fields as well. You don't need to be fancy, don't bother clearing these completely, just take down as many crops ASAP.