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Agriculture is a major industry in the United States, which is a net exporter of food.〔"Latest U.S. Agricultural Trade Data." USDA Economic Research Service. Ed. Stephen MacDonald. USDA, 4 Sept. 2013. Web. 28 Sept. 2013. ==History== (詳細はCorn, turkeys, tomatoes, potatoes, peanuts, and sunflower seeds constitute some of the major holdovers from the agricultural endowment of the Americas. European agricultural practices greatly affected the New England landscape. Colonists brought livestock over from Europe which caused many changes to the land. Grazing animals required a lot of land and food and the act of grazing itself destroyed native grasses, which were being replaced by European species. New species of weeds were introduced and began to thrive as they were capable of withstanding the grazing of animals, whereas native species could not.〔Cronon, William. Changes in the Land : Indians, Colonists, and the Ecology of New England. New York: Hill & Wang, 2003.〕 The practices associated with keeping livestock also contributed to the deterioration of the forests and fields. Colonists would cut down the trees and then allow their cattle and livestock to graze freely in the forest and never plant more trees. The animals trampled and tore up the ground so much as to cause long-term destruction and damage.〔 Soil exhaustion was a huge problem in New England agriculture. Farming with oxen did allow the colonist to farm more land but it increased erosion and decreased soil fertility. This was due to deeper plow cuts in the soil that allowed the soil more contact with oxygen causing nutrient depletion. In grazing fields, the large number of cattle in the New England, the soil was being compacted by the cattle and this did not give the soil enough oxygen to sustain life.〔 In the United States, farms spread from the colonies westward along with the settlers. In cooler regions, wheat was often the crop of choice when lands were newly settled, leading to a "wheat frontier" that moved westward over the course of years. Also very common in the antebellum Midwest was farming corn while raising hogs, complementing each other especially since it was difficult to get grain to market before the canals and railroads. After the "wheat frontier" had passed through an area, more diversified farms including dairy cattle generally took its place. Warmer regions saw plantings of cotton and herds of beef cattle. In the early colonial south, raising tobacco and cotton was common, especially through the use of slave labor until the Civil War. In the northeast, slaves were used in agriculture until the early 19th century. In the Midwest, slavery was prohibited by the Freedom Ordinance of 1787. The introduction and broad adoption of scientific agriculture since the mid-19th century contributed to economic growth in the United States. This development was facilitated by the Morrill Act and the Hatch Act of 1887 which established in each state a land-grant university (with a mission to teach and study agriculture) and a federally funded system of agricultural experiment stations and cooperative extension networks which place extension agents in each state. Soybeans were not widely cultivated in the United States until the early 1930s, and by 1942 it became the world's largest soybean producer, due in part to World War II and the "need for domestic sources of fats, oils, and meal". Between 1930 and 1942, the United States' share of world soybean production skyrocketed from 3% to 46.5%, and by 1969 it had risen to 76%. By 1973 soybeans were the United States' "number one cash crop, and leading export commodity, ahead of both wheat and corn". Significant areas of farmland were abandoned during the Great Depression and incorporated into nascent national forests. Later, "Sodbuster" and "Swampbuster" restrictions written into federal farm programs starting in the 1970s reversed a decades-long trend of habitat destruction that began in 1942 when farmers were encouraged to plant all possible land in support of the war effort. In the United States, federal programs administered through local Soil and Water Conservation Districts provide technical assistance and partial funding to farmers who wish to implement management practices to conserve soil and limit erosion and floods. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Agriculture in the United States」の詳細全文を読む スポンサード リンク
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