Hi WAS,
Just checked my harddrive and I have something from 7 years ago, but it's a bit too messy to share here right now.
What I did there was the following:
1) create second terrain chain in parallel to your original terrain which you offset negatively. The offset amount is the depth of your rice terrace.
2) add strata layer to both chains, make sure strata settings are the same. For example: Depth&Spacing @ 5, steepness 2, buildup 1 and 1 octave.
3) merge the two with a merge shader. Mix value = 0.5 and set mode to subtract.
You can problably swap 1 and 2, but that should be it!