Rice paddies are allowed to dry out prior to harvest and then are kept dry until the next planting season. The soil can get dried and cracked during this season. Just before planting, the paddies are reflooded. At that point the paddy can be like water on concrete, though. The tiller is used to loosen up the concrete and turn it into goey mud again so that the little 12" rice seedlings can be pushed down into the muck and planted. In parts of the world where Yanmar tillers aren't available, water buffaloes (or other animals, including the human kind) are led around and around the paddies to slowly mix water back into the soil to create muck. (Okay, I haven't read an of this so I'm not an authority...just observed rice farming up close over a number of years in Indonesia. I don't know how many rice paddies I've had to walk through throughout the growing season...thousands, probably. BTW, you walk on the dirt levees, not through the muck.)