The Collaborative International Dictionary of English v.0.48:

Productive \Pro*duc"tive\, a. [F. productif, L. productivus fit
   for prolongation.]
   [1913 Webster]
   1. Having the quality or power of producing; yielding or
      furnishing results; as, productive soil; productive
      enterprises; productive labor, that which increases the
      number or amount of products.
      [1913 Webster]

   2. Bringing into being; causing to exist; producing;
      originative; as, an age productive of great men; a spirit
      productive of heroic achievements.
      [1913 Webster]

            And kindle with thy own productive fire. --Dryden.
      [1913 Webster]

            This is turning nobility into a principle of virtue,
            and making it productive of merit.    --Spectator.
      [1913 Webster]

   3. Producing, or able to produce, in large measure; fertile;
      profitable.
      [1913 Webster] -- Pro*duc"tive*ly, adv. --
      Pro*duc"tive*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

productiveness
    n 1: the quality of being productive or having the power to
         produce [syn: productiveness, productivity] [ant:
         unproductiveness]

Moby Thesaurus II by Grady Ward, 1.0:

195 Moby Thesaurus words for "productiveness":
   abundance, access, accession, accomplishment, accretion, accrual,
   accruement, accumulation, achievement, addition, advance,
   affluence, aggrandizement, amperage, ample sufficiency, ampleness,
   amplification, amplitude, appreciation, armipotence, ascent,
   augmentation, authority, avalanche, ballooning, beef, black power,
   bloating, bonanza, boom, boost, bountifulness, bountiousness,
   bringing to fruition, broadening, brute force, buildup,
   bumper crop, charge, charisma, clout, cogence, cogency, compulsion,
   copiousness, crescendo, development, dint, doing, drive, duress,
   edema, effect, effectiveness, effectuality, effectuation,
   elevation, energy, enlargement, execution, expansion, extension,
   extravagance, exuberance, fertility, flood, flow, flower power,
   foison, force, force majeure, forcefulness, full blast, full force,
   full measure, fullness, gain, generosity, generousness,
   great abundance, great plenty, greatening, growth, gush, hike,
   increase, increment, inflation, influence, jump, landslide,
   lavishness, leap, liberality, liberalness, lots, luxuriance,
   main force, main strength, mana, maximum, might, might and main,
   mightiness, more than enough, mounting, moxie, much,
   multiplication, muscle power, myriad, myriads, numerousness,
   operation, opulence, opulency, outpouring, overflow,
   overproduction, performance, pizzazz, plenitude, plenteousness,
   plentifulness, plenty, poop, potence, potency, potentiality, power,
   power pack, power structure, power struggle, powerfulness,
   prepotency, prevalence, prodigality, production, productivity,
   profuseness, profusion, proliferation, puissance, pull, punch,
   push, quantities, raise, realization, repleteness, repletion,
   rich harvest, rich vein, richness, riot, riotousness, rise, scads,
   shower, sinew, snowballing, spate, spread, steam, stream, strength,
   strong arm, substantiality, substantialness, superabundance,
   superiority, superpower, surge, swelling, teemingness, tumescence,
   up, upping, upsurge, upswing, uptrend, upturn, validity, vehemence,
   vigor, vim, virility, virtue, virulence, vitality, wattage, waxing,
   wealth, weight, widening