k, AHD (via Gurunet) might help:
fal·low (făl'ō)

adj.
1. Plowed but left unseeded during a growing season: fallow farmland.
2. Characterized by inactivity: a fallow gold market.

n.
1. Land left unseeded during a growing season.
2. The act of plowing land and leaving it unseeded.
3. The condition or period of being unseeded.

tr.v., -lowed, -low·ing, -lows.
1. To plow (land) without seeding it afterward.
2. To plow and till (land), especially to eradicate or reduce weeds.
[Middle English falow, from Old English fealh, fallow land.]
Now--is that OE word fealh related to fealty?