LEARNING OBJECTIVES
Agriculture changes the environment in many ways, both locally and globally. After reading this chapter, you should understand:
• How agriculture can lead to soil erosion, how severe the problem is, what methods are available to minimize erosion, and how these methods have reduced soil erosion in the United States.
• How farming can deplete soil fertility and why agriculture in most cases requires the use of fertilizers.
• Why some lands are best used for grazing and how overgrazing can damage land.
• What causes desertification.
• How farming creates conditions that tend to promote pest species, the importance of controlling pests (including weeds), and the problems associated with chemical pesticides.
• How alternative agricultural methods—including integrated pest management, no-till agriculture, mixed cropping, and other methods of soil conservation—can provide major environmental benefits.
• That genetic modification of crops could improve food production and benefit the environment but perhaps also could create new environmental problems.
Summary
• The Industrial Revolution and the rise of agricultural sciences have led to a revolution in agriculture, with many benefits and some serious drawbacks. These drawbacks have included an increase in soil loss, erosion, and resulting downstream sedimentation, as well as the pollution of soil and water with pesticides, fertilizers, and heavy metals that are concentrated as a result of irrigation.
• Modern fertilizers have greatly increased the yield per unit area. Modern chemistry has also led to the development of a wide variety of pesticides that have reduced, but not eliminated, the loss of crops to weeds, diseases, and herbivores.
• Most twentieth-century agriculture has relied on machinery and the use of abundant energy, with relatively little attention paid to the loss of soils, the limits of groundwater, and the negative effects of chemical pesticides.
• Overgrazing has caused severe damage to lands. It is important to properly manage livestock, including using appropriate lands for grazing and keeping livestock at a sustainable density.
• Desertification is a serious problem that can be caused by poor farming practices and by the conversion of marginal grazing lands to croplands, Additional desertification can be avoided by improving farming practices, planting trees as windbreaks, and monitoring land for symptoms of desertification.
• Two revolutions are occurring in agriculture, one ecological and the other genetic. In the ecological approach to agriculture, pest control will be dominated by integrated pest management. Agriculture will be approached in terms of ecosystems and biomes, taking into account the complexity of these systems. Soil conservation through no-till agriculture and contour plowing will be emphasized, along with water conservation, through methods discussed in Chapter 20. The genetic revolution is already the subject of controversy, offering both benefits and environmental dangers. Dangers will result if genetic modification is used without considering the ecosystem, landscape, biome, and global context in which it is done.