As it was impossible to raise crops year after year from the same fields without gravely impoverishing the soil, this system was exchanged in some places for another--that of cropping one or two fields and allowing the other to lie fallow. This modification was not always judged requisite to prevent the exhaustion or deterioration of the land; and thus there arose a third--what is termed the "three-field" system, by which out of three arable fields two were under cultivation at the same time, one lying fallow. The third plan was that which ultimately met with most favour. In the early autumn the field that had lain fallow through the summer was ploughed and sown with wheat, rye, or other corn; and in the spring the stubble of the field that had yielded the last crop of wheat was ploughed up, and barley or oats sown in it. The third field, in which the previous crop had been barley, retained the stubble till the early days of June. It was then ploughed up and left in that condition until a fresh crop was sown in the autumn. Professor Cunningham, whose account we here follow, has furnished a convenient chart or diagram which we venture to reproduce as an aid to the comprehension of the subject: I. II. III. Wheat (or rye) Stubble of Stubble of +------------------+--------------+--------------+ _Jan_ | sown | wheat | barley (or | | | | oats) | | | Sow | | |------------------+--------------| | _March_ | | barley | | | | | Plough and | | | |--------------+ _June_ | | | leave fallow | |------------------+--------------| | | | Reap | | _August_ | | | | | | | Plough and | | | |--------------+ _October_ | | | sow wheat | | Wheat | Barley | | +------------------+--------------+--------------+ stubble stubble