agriculture. Agriculture worldwide is facing the daunting challenges of providing for an increasing population that has changing food consumption patterns under the constraints of natural resource scarcity, avoiding environmental degradation, climate change, and a restructuring global economy. In addition, consumers (including food buyers) are increasingly conscious about the sources of their food and how it is produced. Consumer concerns can translate into political and market demands for addressing the challenges. Thus, agriculture appears to be at a pivotal stage in terms of societal demands for agricultural systems with improved sustainability—that is, systems that address and balance social, economic, and environmental performance, and increase robustness in the face of new challenges.

There are growing concerns about whether the trends of increasing productivity per acre of land can continue while maintaining or restoring the natural resource base upon which agriculture depends. Similarly, researchers and some members of the public are increasingly worried about many of the unintended negative consequences of agricultural production—for example, the effect of agriculture on environmental quality and ecosystem functioning, the potential risks of agricultural pollutants or risks of contamination of food and water by agricultural input to human health, and the safety and nutritional content of the food produced. Some observers raise the issues of how modern agriculture affects the well-being of farming communities, farm families, farm laborers, and livestock (Friedland et al., 1991; Vitousek et al., 1997). Those concerns have caused observers to question whether U.S. agriculture can continue to supply adequate quantities of reasonably priced food, feed, and fiber using conventional production methods. What are the tradeoffs and risks that will be required to maintain, and even increase, growth in productivity?

Many unintended consequences of agricultural activities can be thought of as externalized costs of production, which are real, but mostly unaccounted for in productivity measures or internal financial budgets of farm enterprises. Societal concerns raise important public policy questions regarding the type, scale, and organization of U.S. agriculture that can best meet society’s needs in the future. Those concerns generate interest in alternatives to the current system of agricultural production that might increase the sustainability and broader performance of modern farming systems. The two major concerns of resource sufficiency and unintended consequences can be summarized in two questions: Are current agricultural practices and systems sustainable? If not, how can agriculture be moved toward a more sustainable trajectory?

The purpose of this report is to identify what is known about farming practices and systems and their ability to address the identified concerns. This chapter provides a brief overview of how U.S. agriculture has evolved over the years to the current state. Despite the many positive changes (for example, increased productivity), farmers now face a different set of challenges related to environmental, social, and economic concerns. This chapter also discusses those challenges.

A BRIEF HISTORY OF U.S. AGRICULTURE

U.S. agriculture’s current structure and organization is a product of a long evolution (Batie, 2008). Since World War II, increased mechanization, rising productivity, and growth in nonfarm employment opportunities combined to produce more than a 60 percent drop in the number of farming operations and a doubling in average farm size in the United States (Gardner, 2002). Between 1982 and 2002, most types of crop farms have at least doubled in size, and the average size of livestock herds has increased by 2–20 times, depending on species (MacDonald and McBride, 2009). Growth in scale and productivity among the remain-



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