A free history of 20th century agriculture

The abstract from Carolyn Dimitri, Anne Effland, and Neilson Conklin at USDA's Economic Research Service (.pdf):

The structure of farms, farm households, and the rural communities in which they exist has evolved markedly over the last century. Historical data on a range of farm structure variables—including the value of agricultural production, commodity specialization, farming-dependent counties, and off-farm work—offer a perspective on the long-term forces that have helped shape the structure of agriculture and rural life over the past century. These forces include productivity growth, the increasing importance of national and global markets, and the rising influence of consumers on agricultural production. Within this long-term context of structural change, a review of some key developments in farm policy considers the extent to which farm policy design has or has not kept pace with the continuing transformation of American
agriculture.