I’ve been adding fields in an area near me. I’ve carefully traced the edges of just the tilled land, leaving spaces where there are tracks, ditches, and field margins. See here: https://osm.org/go/eu7auQi1
This takes ages but I’d understood from an authoritative comment somewhere (where in the world of OSM I can’t tell you!) that this was the right approach.
I’ve seen elsewhere (here) a more liberal approach, where the landuse area is much less fine-grained, in particular with hedges drawn on top of the landuse area, rather than tracing an area between them.
That would save many hours, so I’d prefer that route, but before I go there could I have advice about whether it’s right? I’ve read the wiki and can’t see an answer.
There are preferences and some no-goes: e.g. do not destroy other’s work.
My personal preference is to map elements that are clearly line elements as lines over and accross the larger area alement as farmland.
E.g. hedges, paths, tracks, unclassified roads, drains.
This a: for reasons of simplicity, ease and speed
and b: if you leave empty space between a line element and landuse, at high zoom factors a 'vacuum’ undefined area shows up, which isn’t the case if the line element is drawn over the landuse, which, I think, is neat.