The farm is a major marketplace for millions of tons of synthetic fertilizers and pesticides (杀虫剂),and advanced machinery and the fuel required to run it. The modern super farm, large and highly capitalized, is resource dependent compared with the diversified small farms that were once dominant. On diversified farms, major energy needs may be supplied by resident humans and animals. Soil fertility may be maintained by alternating cash crops and restorative crops, and also by returning animal manure(肥料) to the soil. This farming model of relatively self- sufficient agriculture, and the way of life associated with it, are still economically viable(可行), as demonstrated by prosperous Amish farmers and other practitioners of "alternative" agriculture. Particularly relevant to today"s mainstream agriculture are the energy-saving practices on large "organic" farms, which are thoroughly mechanized but which minimize the use of pesticides and synthetic fertilizers. By comparison, mainstream American agriculture has until lately been careless in its use of energy, water, and land. When fossil energy was cheap, applications of fertilizers and pesticides paid large dividends, so farmers were encouraged to use these products. Soon most farmers used too much fertilizer and pesticide. Farmers in dry regions enjoyed an era of cheap water, obtained from publicly subsidized irrigation systems or from pumping groundwater using, inexpensive energy. The soil too was expendable as demand grew for U.S. agricultural products. The period of extraordinary profligacy in the use of soil, water, and fossil fuels may well be at an end. The new structure of large farms is quite sensitive to cost factors. These adaptive farms, whose development was assisted by public tax, subsidy, and research policies, have access to capital, technologies, and management skills, enabling them to switch relatively quickly to resource-conserving practices—for example, to a low-tillage system that requires less fuel, that shepherds soil moisture, and that may reduce soil erosion(侵蚀). It seems likely that federal programs that have enlarged our farms, therefore, have had a further result of creating the potential for a more conserving agriculture. With respect to energy use, for example, energy costs per unit of output are lower for large farms, mainly because these farms quickly economized on energy as costs rose. In the future, according to one authoritative assessment, "agricultural production is likely to use capital and land more intensively but energy, fertilizer and labor less intensively."
单选题
The main difference between the modem superfarm and diversified farms is______