The balk, back, bauk (Lowland Scots), leum-iochd or bailc/bac (Scottish Gaelic) was a strip of a corn field left fallow.
or gobhar bhacach (the goat of the balk) always led to an exciting competition among the reapers in the last field.
In Heart of Midlothian (1818) by Walter Scott, he glosses it as "an unploughed ridge of land interposed among the corn" Gregor's Folk-lore of North East Scotland (1881) says: Bauks were also used as boundaries between neighbours' land.
George Robertson's General view of Agriculture in Perth (1799) says: "Large slices of land are left unploughed, as boundaries between the alternate ridges of neighbours, in the same plough-gate; which are a perpetual nursery of weeds, besides the loss of so much land lying waste.
However, the word is recorded in the 1920s north east Scotland, as referring to a path between fields, obviously a residual use with a slightly different meaning.