Actually fishing line would be much easier and lighter than rope. And, nope, it ain't rocket science except to those who can't tell rocket science from magic (or little green men).
Right. Good idea. Especially since we'll be backpacking this stuff across the field while walking on stilts.
Also, the actual lines in the crops can be made very precise by using the right kind of plank-snowshoes. It would take a little experimenting, but once you had the optimum size figured out for easy walking, all you need is to have the pair of snowshoes be the width of the channel you want to stomp out, and then you walk along with a sliding motion, keeping the inner edges of the snowshoes in contact, so that you always had a constant width of flattened crops. All it takes is a bit of practice, and you too can be as exact as the aliens.