Complex sentence: As explained in the "Aobo Tu", workers sprinkled sea water on the fields which then filtered through sand or fine ash into pits, or perhaps it could have been "earth salt" from soil.
Split into simpler sentences: As explained in the "Aobo Tu", the method actually involved first sprinkling sea water on the fields, which then filtered through sand or fine ash into pits. Perhaps, rather than being salted with sea water, it could have been "earth salt" from soil.