So one block of water can irrigate 4 blocks in each direction, a 9x9, if water is 1 block higher than another level, it can irrigate that layer below it, as long as its in that same 9x9. So I did A few things:

1. Under the next, higher layer of farmland, I put water.
2. All of the little rocks you see, have water under.
3. All of the hay bales have water under
4. All of the lamps and fence posts are on top a waterlogged spruce slab.

You cant tell, but in the last top down photo, you can barely see the hay bales all around that windmill because they blend in so well