Arable farming, particularly where the plough is the main means of cultivating, has profoundly altered the soil by both adding and removing plant nutrients, reducing acidity with lime, draining excess soil moisture with underground pipes, removing stones, and changing the soil structure. More fundamental changes have been brought about by the removal of surface water. Long and painstaking drainage schemes, notably in the English fenlands, the Dutch polders and inland lakes, and in the Po valley of northern Italy, have converted waterlogged lowlands into first-class farmland. Equally profound have been the changes brought about by bringing water to arid and semi-arid regions; irrigation schemes in Iraq, Egypt, Pakistan and elsewhere have all transformed the land and landscape. Steep slopes and high altitudes present great obstacles to the farmer, but terracing has made arable farming possible in many parts of upland Asia and North America.
Agriculture, in short, transforms the environment; other chapters in this
book deal in detail with these matters. The purpose of this chapter is not to
describe how agriculture changes the environment, but to explain why
changes in agriculture have come about.