A single crop grown repeatedly on the same area of land allows the expensive back-up facilities of capital and machinery to be spread over a number of years, but does raise problems of loss of fertility or build-up of pests. This singleminded approach can be tempered by the use of a sequence of enterprises which are mutually beneficial.
A rotation is devised to suit a particular set of circumstances and requirements. At its simplest it is to be seen in the slash and burn technique. As simple, but more productive, is the system known as alternate husbandry, in which an area of land is used for a short time for arable production, and then sown to grass and grazed for a number of years, the animal manure making a significant contribution to the fertility of the land. There is increasing evidence for the practice of crop rotations even in the very earliest settlement areas, but the first references to alternate husbandry appear in the agricultural writings of Columella in the first century AD. It was later practised by the Cistercians in France, where as early as 1400 they were advocating five years of grass, followed by two years of corn and then reseeding with grass.
More complicated rotations were created to resolve more difficult problems and in Europe all the traditional constituents of rotations were known and being used at least as early as the Roman period. Legumes, turnips and corn were all documented if not widely grown. In mediaeval East Anglia extremely complicated rotations of fourteen-year duration have been recorded. It therefore seems likely that formal rotations were in use over a much wider area, and at a much earlier period than the seventeenth-century English writers would suggest. By 1880 leguminous crops were an established part of the farming regime throughout Europe, and they represented a significant proportion of the total arable acreage. This situation is significantly different from that of a hundred years earlier and is an indication of the recognition of the nitrogen fixing properties of this crop. Over the same period the reduction in the acreage left fallow is significant and highlights the benefits derived from the change of rotation made possible by the additional use of legumes, not only in terms of increased yield per acre, but also in terms of the increase in the numbers of productive acres.