My grandmother always cut out a piece of sod the same size as the nest to line the bottom of the next when setting a hen on eggs to hatch. Hay was then added over the sod. The point of the sod was to maintain moisture. She would then sprinkle water on the nest occasionally during the hatching cycle to keep the sod a little moist. I have always done it this way. I know with incubators you have to keep the moisture level up.
