ABSTRACT
This chapter examines the environmental impacts of agriculture and the factors that influence food security, which exists "when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life". It reviews problems that reduce food security, such as water scarcity, competition from biofuel production, overfishing, inadequate food distribution, overuse of fertilizers, and land grabbing. In the twentieth century food security was enhanced by the Green Revolution, which greatly increased global food production and reduced the frequency and severity of famines. The United States is the world's largest food producer and exporter, and it is where modern industrial agriculture originated. Before the Green Revolution of the twentieth century, farmers practiced ancient methods of crop rotation and use of manure and crop residue as organic fertilizer. The American agricultural system experienced further changes in the 1970s.
