The Collaborative International Dictionary of English v.0.48:

Tilth \Tilth\, n. [AS. til?, fr. tilian to till. See Till to
   cultivate.]
   1. The state of being tilled, or prepared for a crop;
      culture; as, land is good tilth.
      [1913 Webster]

            The tilth and rank fertility of its golden youth.
                                                  --De Quincey.
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   2. That which is tilled; tillage ground. [R.]
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            And so by tilth and grange . . .
            We gained the mother city.            --Tennyson.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tilth
    n 1: the state of aggregation of soil and its condition for
         supporting plant growth
    2: arable land that is worked by plowing and sowing and raising
       crops [syn: cultivated land, farmland, plowland,
       ploughland, tilled land, tillage, tilth]