Which of the following agricultural methods led to the greatest yield?

The three-field system is a type of crop rotation. The effect of the three-field system was to allow fields to lie fallow or grow crops that put nutrients in the soil so as not to wear out the soil. A field of grain, one of legumes, and a fallow field were rotated with each growing season. It allowed for more crops to produce more food and led to population growth.

If a crop was not rotated, then the nutrient level in the field would go down with time. The yield of the crop from the field decreased. Using the four field system, the land could not only be "rested", but also could be improved by growing other crops. Clover and turnips grown in a field after wheat, barley or oats, naturally replaced nutrients into the soil. None of the fields had to be taken out of use whilst they recovered. Also, where animals grazed on the clover and turnip fields, eating the crop, their droppings helped to manure the soil.