Fallow (from the same root as Ger. fahl or falb, expressing a pale dun, tawny colour). This word sometimes signifies waste, untilled land; but usually it is applied to land that is ploughed and otherwise cultivated for a season without being cropped. The most of the wheat raised by the Romans was sown after the land was fallowed; indeed, the usual rotation was fallow and wheat alternately. It was only fertile soils that could long support such an exhausting system; hence resulted the decreasing produce which the later Roman agricultural authors so often speak of and lament.
The fallowing of land was introduced into all the countries which fell under the dominion of the Romans. Britain during their sway soon exported large quantities of wheat, and for centuries after the Romans left no other mode of cultivating the land was followed. It may here be observed that, wherever the system of fallowing without giving manure to the crops is practised, it necessarily supposes that the soil is at least moderately fertile. This system is most successful on argillaceous soils, which are retentive of organic manure, and which cannot be cleaned by any other method. The destruction of weeds, such as couchgrass (Triticum repens) with its long jointed roots, is the first great object of fallowing. The exposure of the soil-substance to the weathering action of the air and the rest given to the land are minor objects. The loss from washing out of valuable soluble substances, more especially nitrogen, by rain, is a serious disadvantage of fallowing; and this, along with the possibility of the land becoming more and more foul with weeds during a wet summer, makes the benefits of the practice extremely doubtful, unless under exceptional circumstances.
It was long before fallowing was introduced to any extent in Scotland; but about the beginning of the 19th century it was largely practised. Owing, however, to the draining of the soil and the extension of the green-cropping system, it is now confined to the most retentive clay-soils, where it affords the only means of thoroughly cleaning the land. Sometimes as many as three or four ploughings are given in summer before the seed is sown in autumn. In old cultivated countries land is commonly so much reduced in its organic matter that fallows require to be dressed with farm-yard manure, rape-dust, or guano, to obtain satisfactory crops. Since the general introduction of green crops the term fallow has departed in some measure from its original meaning. These crops are sown on what was formerly the fallow-break, and are now often styled fallow-crops. The land, no doubt, receives in some measure a fallowing; it is freed from weeds, and allowed to rest from the growth of grain crops. Bastard-fallowing is a term which is used in Scotland when hay-stubble is ploughed up in the end of summer, freed from weeds, and sown with wheat in autumn.