Monoculture is the agricultural practice of planting, cultivation, and harvesting of a single species of crop in a specified area. It has been common for a long time in many places, such as plantations or vineyards, but it has become far more widespread during the last 30 or 40 years, especially in the production of cereals. This is as a result of the availability of machinery for harvesting large quantities very quickly. There are also many fertilizers which restore fertility to the soil, so that crop rotation (whereby different crops are grown in the same fields every year or so) is unnecessary. Monoculture has created problems, however, as dependence on one crop can be serious if the price suddenly falls because of a glut, or if new pests invade the crop. Moreover, it is being realized that monoculture harms and possibly ruins the soil, in spite of the addition of artificial fertilizers. Monoculture in such areas as the prairies in Canada and the US, the steppes in Russia, and East Anglia in the UK is now declining slightly, and there are signs of a return to crop rotation methods.