From the second edition (1989):
Sc. and north. dial.
(dɑːg) Also 5 dawerk, dawark, 8 daurk, 9 daark, dark, darrak, darroch, dargue, daurg, [A syncopated form of daywerk, or daywark, daywork, through the series of forms dawark, *da'ark, dark, darg, the latter being now the common form in Scotland.]
A day's work, the task of a day; also, a defined quantity or amount of work, or of the product of work, done in a certain time or at a certain rate of payment; a task.
c1425 Wyntoun Chron. ix. xiv. 44 (Jam.) That duleful dawerk that tyme wes done. 1489 Act. Audit. 147 (Jam.) Ffor the spoliatioune of vi dawarkis of hay. 1535 Stewart Cron. Scot. II. 596 For that same darg and deid. 1605 in Pitcairn Crim. Trials Scot. II. 451 Fourscoir dargis of hay. 1787 Burns Auld Farmer's Salut. xvi, Monie a sair daurk we twa hae wrought. 1794 Statist. Acc. Scot. XII. 300 A darg of marl, i.e. as much as could be cast up by the spade in one day. 1818 Scott Hrt. Midl. xxvi, I have a lang day's darg afore me. 1832–4 De Quincey Cæars Wks. 1862 IX. 51 You did what in Westmoreland they call a good darroch. 1851 Greenwell Coal-tr. Terms Northumb. & Durh. 21 Darg, a fixed quantity of coal to be worked for a certain price‥the general term in use about Berwick. 1878 Cumbrld. Gloss., Darrak (Centre), dark (S.W.), darg (North C.), day's work. 1875 Ruskin Fors Clav. VI. 8 Lett. 61 And goes out himself to his day's darg.
Hence ˈdarg-days, days of work done in lieu of rent or due to the feudal lord. ˈdarger, ˈdarker, ˈdargsman, day labourer. ˈdarging, working as a day-labourer.
1803 Jamieson Water-Kelpie iv. in Scott Minstr. Sc. Bord., The darger left his thrift. 1807 J. Stagg Poems 64 The laird and dar'ker cheek by chowle, Wad sit and crack of auld lang seyne. 1788 R. Galloway Poems 119 (Jam.) Glad to fa' to wark that's killing, To common darguing. 1885 in D. H. Edwards Mod. Sc. Poets Ser. viii. 44 A bargain‥for drainin' or for dargin'. 1845 Whistle-binkie Ser. iii. (1890) I. 418 Warnin dargsmen to put on their claes.