Like mangolds, turnips are capable of producing very large quantities of digestible stock food per acre; and where the pro duction of such nutriment is the principal object in cultivating the crop, as in certain systems of sheep farming and in dairying with little arable land, turnips may occasionally be grown twice in succession on the same field. In most cases, however, turnips occupy a place in the rotation in which they serve as a fallow crop, affording opportunities for eradicating weeds that have ap peared in preceding corn crops, and otherwise serving as a means of restoring the condition of the land for future corn cultivation.
In the preparatory cultivations for turnips, the object of creat ing soil conditions favourable to the growth of the crop is gener ally more or less subservient to the processes of cleaning and manuring. The two objects can best be combined when it is possi ble to clean the corn stubble in autumn and to apply the yard manure before the deep ploughing in early winter or before a second or cross ploughing in February. When autumn cleaning is impossible, .it is customary to defer the application of the yard manure until spring, when it is applied in the ridges on which the roots are drilled, after the weeds have been extracted by appropriate operations. In some cases, particularly in districts of low rainfall, turnips grown on land that has been cleaned in spring are sown on the flat and receive artificial manures only. The artificials applied in the latter case are typically i cwt. sulphate of ammonia, 5 cwt. superphosphate and 1 cwt. muriate
of potash per acre.
Swedes are drilled in May in districts north of the Trent and in June farther south, where earlier sowing predisposes the crop to attack of turnip flea beetle and mildew. Yellow turnips are sown about a month later than swedes, but are harvested—where not consumed on the land by sheep—about the same time, Novem ber. White turnips may be sown at different times in the sum mer : they are almost invariably fed without previous storage. White turnips are also frequently sown broadcast and not further cultivated or thinned. Swedes and yellows, however, are usually drilled in rows about 24 in. apart and afterwards thinned out to 10–in. intervals, and horse- and hand-hoed two or three times during the summer.
Swedes contain a higher percentage of dry matter, and also of digestible nutrients, than yellow turnips, which in their turn are richer than white turnips. Ton for ton, therefore, the order of feeding value is: swedes, yellow turnips, white turnips.
There is no extensive trade in swedes, though there may occa sionally be small farmer to farmer sales, and crops may be sold for feeding off on the field. This applies equally to turnips. In some districts also swedes may be sold to green-grocers, much of the south Lancashire crop, for example, being consumed in the towns. White turnips are of course specially grown in fairly considerable quantities for table use. (See VEGETABLE : Culture in the United States.) (J. R. B. ; H. C. L.)