<P> One of the most important innovations of the British Agricultural Revolution was the development of the Norfolk four - course rotation, which greatly increased crop and livestock yields by improving soil fertility and reducing fallow . </P> <P> Crop rotation is the practice of growing a series of dissimilar types of crops in the same area in sequential seasons to help restore plant nutrients and mitigate the build - up of pathogens and pests that often occurs when one plant species is continuously cropped . Rotation can also improve soil structure and fertility by alternating deep - rooted and shallow - rooted plants . Turnip roots, for example, can recover nutrients from deep under the soil . The Norfolk System, as it is now known, rotates crops so that different crops are planted with the result that different kinds and quantities of nutrients are taken from the soil as the plants grow . An important feature of the Norfolk four - field system was that it used labour at times when demand was not at peak levels . </P> <P> Planting cover crops such as turnips and clover was not permitted under the common field system because they interfered with access to the fields . Besides, other people's livestock could graze the turnips . </P> <P> During the Middle Ages, the open field system had initially used a two - field crop rotation system where one field was left fallow or turned into pasture for a time to try to recover some of its plant nutrients . Later they employed a three - year, three field crop rotation routine, with a different crop in each of two fields, e.g. oats, rye, wheat, and barley with the second field growing a legume like peas or beans, and the third field fallow . Normally from 10--30% of the arable land in a three crop rotation system is fallow . Each field was rotated into a different crop nearly every year . Over the following two centuries, the regular planting of legumes such as peas and beans in the fields that were previously fallow slowly restored the fertility of some croplands . The planting of legumes helped to increase plant growth in the empty field due to the bacteria on legume roots' ability to fix nitrogen (N) from the air into the soil in a form that plants could use . Other crops that were occasionally grown were flax and members of the mustard family . </P>

What was not a result of the agricultural revolution