When looking up more details it seems that it's actually not possible to make them mechanically. It's considered one of the disadvantages despite their simple and cheap implementation.

Edit: I think you're also applying a western image of what farmland is to this situation. I don't think I can do it justice so I highly recommend you look up some of these videos to get better picture, it's quite interesting and at least some glimmer of hope to see that some land can be reclaimed from erosion and desertification.