The Collaborative International Dictionary of English v.0.48:

Unfruitful \Un*fruit"ful\, a.
   Not producing fruit or offspring; unproductive; infertile;
   barren; sterile; as, an unfruitful tree or animal; unfruitful
   soil; an unfruitful life or effort. -- Un*fruit"ful*ly,
   adv. -- Un*fruit"ful*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unfruitful
    adj 1: not fruitful; not conducive to abundant production [ant:
           fruitful]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "unfruitful":
   acarpous, arid, barren, celibate, childless, desert, desolate,
   drained, dried-up, dry, effete, 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, unplowed, unproductive,
   unprolific, unsown, untilled, virgin, waste, wasted,
   without issue