WordNet (r) 3.0 (2006):

unplowed
    adj 1: (of farmland) not plowed; "unplowed fields"; "unbroken
           land" [syn: unplowed, unploughed, unbroken] [ant:
           ploughed, plowed]

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "unplowed":
   acarpous, arid, barren, celibate, childless, desert, desolate,
   drained, dried-up, dry, exhausted, fallow, fruitless, gaunt,
   gelded, impotent, ineffectual, infecund, infertile, issueless,
   jejune, leached, menopausal, nonfertile, nonproducing,
   nonproductive, nonprolific, sine prole, sterile, sucked dry,
   teemless, uncultivated, unfertile, unfruitful, unproductive,
   unprolific, unsown, untilled, virgin, waste, wasted,
   without issue