So, I stopped playing for a couple of years, and now back to playing.
Educate me on sheep poop.
Baby sheep gets fed.
Turns into adult sheep and gives poop.
Then never poops again?
Can I feed them to get more poop?
Is this the only way to make ferilizer?
The adults sheep can be shorn by shears.
Take the fleece.
Feed shorn sheep with baked bread.
Then u can get poop. : )
ps: Leave enough space for sheep to poop 
There is another way to make soil/fertilizer, that requires no poop, but it requires for you to have allot of iron and diggings(holes) atound your town. It uses boxes, worms, dug-up soil, and shredded vegetables.
You don’t have to dig a lot, necessarily. Couldn’t you just leave a 3/4 dug hole and scoop out the dirt w a basket when it respawns?
Yes you can, but it consumes time to replenish the digged up soil and what ever tools you are using to dig them, if you have to dig that is( i mean if you forget to scoop with basket). Though I’m not sure if you can place the soil in the chests with a basket. 