FALLOW, land ploughed and tilled, but left unsown, usually for a year, in order, on the one hand, to disintegrate, aërate and free it from weeds, and, on the other, to allow it to recuperate. The word was probably early confused with "fallow" (from O. Eng. fealu, probably cognate with Gr., grey), of a pale-brown or yellow colour, often applied to soil left unfilled and unsown, but chiefly seen in the name of the "fallow deer." The true derivation is from the O. Eng. fealga, only found in the plural, a harrow, and the ultimate origin is a Teutonic root meaning "to plough," cf. the German falgen. The recognition that continuous growing of wheat on the same area of land robs the soil of its fertility was universal among ancient peoples, and the practice of "fallowing" or resting the soil is as old as agriculture itself. The "Sabbath rest" ordered to be given every seventh year to the land by the Mosaic law is a classical instance of the "fallow." Improvements in crop rotations and manuring have diminished the necessity of the "bare fallow," which is uneconomical because the land is left unproductive, and because the nitrates in the soil unintercepted by the roots of plants are washed away in the drainage waters. At the present time bare fallowing is, in general, only advisable on stiff soils and in dry climates. A "green fallow" is land planted with turnips, potatoes or some similar crop in rows, the space between which may be cleared of weeds by hoeing. The "bastard fallow" is a modification of the bare fallow, effected by the growth of rye, vetches, or some other rapidly growing crop, sown in autumn and fed off in spring, the land then undergoing the processes of ploughing, grubbing and harrowing usual in the bare fallow.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)