ABSTRACT
SINCE the earliest times, the progress of agriculture hasbeen hampered by an important physical fact-the ten-dency of the soil to lose its fertility under continuous cultivation. If crops are grown without intermission on a piece of ground, the elements of plant nutrition in the soil become gradually used up, and if the process is continued long enough, the land will be stricken with barrenness. How to arrest or overcome this tendency has been the standing problem of agriculturists in all ages. Prior to the modern period, the methods employed for this purpose were principally three: (r) the use of animal manure; (2) the practice of fallowing; (3) the alternation of crops. Of these, the first is undoubtedly the best. Nothing restores the fertility of exhausted soil like animal manure. But for obvious reasons, the amount of it at the disposal of farmers is limited. This was even more true in the Middle Ages than it is to-day. Owing to the absence of winter-roots and the consequent difficulty of keeping animals alive during the winter season, the medieval farmer could not rear more than a limited number of cattle. The only winter-fodder available was the hay which had been raised during the summer, and as this was never sufficient to feed all his animals, the farmer had to make a rough calculation of the number of beasts he thought he could keep alive during the winter and slaughter the remainder.! The small number of cattle on the medieval farm restricted the supply of natural manure and compelled the adoption of other methods of restoring the exhausted fertility of the soil. Of these, the most important was fallowing. Each field was left uncultivated every two or three years. This gave the soil a rest and allowed it time to recuperate. During the fallow period, the field was ploughed up two or three times, partly to clear it of weeds, partly to expose the
15 earth to the fertilizing influences of the sun and air. The practice of fallowing was supplemented by the alternation of crops. Different crops take different elements from the soil, and if, say, wheat and barley are grown alternately on the same piece of land, it retains its fertility longer than if one crop is grown continuously. Alternation of crops, however, did not permit the farmer to dispense with fallowing, and in the three-field system, the most advanced form of agriculture known in Europe previous to the eighteenth century, fallowing and alternation of crops were combined. The cultivated land was divided into three large portions, technically known as ' fields', each of which was cultivated under a three-course rotation as in the following table:
The three-field system was a form of intensive cultivation. It solved the difficult problem which faced agriculturists when land became scarce and it was no longer possible to take in virgin soil in place of that which was already exhausted. But the system was a wasteful one since it involved leaving onethird of the cultivated area idle every year. This obvious defect in agricultural practice was not removed until the eighteenth century, when the introduction of green crops and winter-roots made it possible to dispense with the fallowing process. The importance of this reform can scarcely be exaggerated. It led to a complete revolution in the art and practice of agriculture, and indirectly produced important changes in the social and economic position of the cultivators of the soil.
