Fertile Soil Pile is created by dumping a basket of soil or soil-filled backpack on the ground. Using a Clay Bowl will get 3 Bowl of Soil. It can be tilled using a hoe. A pile of 1 soil requires 2 tillings to get Deep Tilled Row. A pile of 3 soil, or one soil on a hardened row, only requires 1 tilling.
Previously
Note: It used to be considered a waste to till a soil pile with 3 bowls worth of soil since it used to give the same as a 2 soil pile.