ABSTRACT
It had long been recognised that unless fields were intensively manured they needed intermittent periods of rest; in other words, to avoid exhausting the soil it was not only necessary to vary the crop but also to interrupt cultivation altogether for a time. Although now quite outmoded, in its context the idea was reasonable; the scarcity of dung and the narrow choice of crops available for rotation (narrow because of the necessary predominance of cereals) meant a mere change of crop was insufficient to refresh the soil and keep the weeds at bay. This general rule, learned from experience, was applied in a variety of ways. It was obviously necessary to introduce some kind of order, more or less rigidly observed, into the sequence and treatment of the active and passive periods. Many permutations are possible and several were in fact used-the various systems of crop rotation.
