摘要：The U.S. farm sector has seen considerable structural change in both farm size and number of farms over the last half century. The number of farms has steadily declined from 5.4 million in 1950 to 2.1 million in 1996, while the value of products (measured in 1992 dollars) has increased from $54.8 billion to $191.7 billion during the same period (Harrington et al., 1998). The trend towards fewer, but larger farms accelerated during the 1950's and 1960's, but has slowed somewhat since the 1970's. The latest census data show that the long-term trend of declining farm numbers, slightly declining land in farms, and increasing average farm size continued throughout the 1980's and 1990's (1997 Census of Agriculture, U.S. Department of Agriculture). Thus, farms have become fewer and larger and the movement toward greater production concentration has been a persistent feature of production agriculture. The exhaustive list of factors affecting the U.S. farm structural change includes technological change, economies of size, farm policy and programs, tax laws, and credit and income programs (Cochrane, 1993; Ramussen and Stanton, 1993; Sumner: 1990, Tweeten, 1993). Major contributions to this literature include Gardner and Pope (1978) for technological change, Lu (1985), and Kislev and Peterson (1982) for bias toward machinery in technological change, Hallam (1993), Miller (1979), and Miller et al. (1981) for economies of scale, and Leathers (1992) for government farm programs.
