Chapter 23 : Biotechnology and Sustainable Agriculture

Energy use in agriculture. Agricultural practices use fossil fuels to power farm equipment and other vehicles, dry crops, and control the temperature in animal production facilities. Fossil fuels are also used in the production of chemical inputs, such as fertilizers and pesticides.

Water pollution. The primary water pollution problem in the United States is sedimentation. The major contributor to sedimentation is water runoff from cropland and overgrazed pastures. (Photograph by Linda Betts, courtesy of Natural Resources Conservation Service, USDA.)

Fungal pathogens, Bt corn, and mycotoxins. Because Bt corn provides better protection against insect damage, there are fewer holes in the plant that can be invaded by fungal pathogens, such as Fusarium. In the study shown, researchers at Iowa State University measured both the incidence of infection and the amount of mycotoxins secreted by Fusarium. Comparable results showing decreased levels of mycotoxins in Bt corn have been documented by scientists in other U.S. universities and in Argentina, France, Italy, Spain, and Turkey.

Soil conservation. Low-tech forms of conservation that decrease erosion and increase the efficiency of water use include contour farming, strip farming, and terracing (upper right corner). The contours redirect water laterally, thus eliminating runoff. Interspersing thin strips of alfalfa (green) between large expanses of highly erodible cornfields (tan) creates a buffer, especially against wind erosion. Terrace farming helps prevent erosion and water runoff when the field is located on a slope. (Photograph by Tim McCabe, courtesy of Natural Resources Conservation Service, USDA.)

Irrigated cropland. Approximately 40% of the world's food supply grows on irrigated croplands. The number of cropland acres that depend on irrigation has increased by approximately 70% in the past 25 years. According to the United Nations Food and Agriculture Organization, only four countries account for 50% of the irrigated cropland: India, China, Pakistan, and the United States.

Plant root hairs. (A) Plants absorb water through microscopic root hairs that cover their roots. Like the microvilli in your intestine, root hairs greatly increase the surface area available for absorbing nutrients. (B) Scanning electron micrograph of a single root hair showing clearly that it is an extension of root epidermal cells (red). The fluorescence stain the electron microscopist used reveals actin filaments (green) that are identical to those in animal cells. (Micrograph A courtesy of Nina Allen, North Carolina State University; micrograph B by Elison Blancaflor of the Nobel Organization, courtesy of the Samuel Roberts Noble Foundation, Ardmore, Okla.)

An open plant stomate. Plants acquire carbon dioxide for photosynthesis and release oxygen through highly specialized structures, the stomata. Leaves contain thousands of stomata per square inch. Unfortunately, when stomates are opened for gas exchange, water that has been absorbed by the roots is lost. (Photograph copyright Dennis Kunkel Microscopy, Inc.)

Plant cell.

Fertilizer application to cropland. Chemically synthesized fertilizers contain three essential plant nutrients: nitrogen, phosphorus, and potassium. The two most important elements that limit agricultural productivity globally are nitrogen and phosphorus.

Mycorrhizae. (A and B) The fungal threads, or hyphae, of the fungus species in mycorrhizal associations form a dense network around the plant roots. (C) Some hyphae invade the root cells, which is similar to the first stage of nodulation exhibited by nitrogen-fixing bacteria that develop symbiotic relationships with plants. The dark-blue dots in panel B are nutrient storage vesicles of the fungus. (Photographs courtesy of Randy Molina, U.S. Forest Service, USDA [A], and Agricultural Research Service Eastern Regional Research Center, USDA [B and C].)

Biological control. (A) Predatory insects. Ladybird beetles are beneficial insects in agroecosystems because they prey on aphids, many of which are crop pests that transmit plant pathogens. (B) Parasitoid wasps. A number of parasitoid wasp species lay eggs in lepidopteran larva, such as this tobacco hornworm. The wasp larvae feed on the internal tissues of the lepidopteran larvae and then emerge as pupae. (C) The USDA scientist shown is examining species of fungi that may be useful in weed control. (Photographs A and C by Scott Bauer, courtesy of Agricultural Research Service, USDA.)

Triggering molecules for self-defense. Grapefruit leaves that were sprayed with naturally occurring molecules that trigger the plant's self-defense systems defended themselves against fungal diseases. Those that were not sprayed were infected. (Photograph by Keith Weller, courtesy of Agricultural Research Service, USDA.)

Recruiting parasitoids. When plants are attacked by herbivores, they secrete volatile compounds that trigger the self-defense systems of other plants and also alert parasitoid wasps and insect predators. This parasitoid wasp, which is only 1/4 inch long, is laying an egg in an insect pest. (Photograph by Scott Bauer, courtesy of Agricultural Research Service, USDA.)

Global area of transgenic crops. The amount of cropland planted in transgenic varieties has increased every year since the first transgenic crop became available for large-scale commercial use in 1996. One hectare is approximately 2.47 acres. Therefore, the total number of acres planted in transgenic crops in 2003 was 167.2 million acres.

Figure 23.15Acres of transgenic crops grown by U.S. farmers.

Figure 23.16Cropland acreage changes from 1700 to 2000. (Data courtesy of the United Nations Food and Agriculture Organization.)

Corn and teosinte. In Mexico, the center of origin for corn (or maize), corn (A, upper left) readily hybridizes with its wild relatives, the teosintes (A, lower right, and B). (See Figure 1.6 for the relative sizes of modern corn and teosinte.) (Photographs copyright Klaus Ammann.)

Figure 23.18Many crop pests have become resistant to synthetic chemical pesticides. Over 500 insect pests are resistant to at least one insecticide, and over 100 weed species have evolved resistance to at least one herbicide.

An adult corn rootworm feeding on corn silk. (Photograph by Tom Hvalty, courtesy of Agricultural Research Service, USDA.)

A corn rootworm larva. (Photograph courtesy of Agricultural Research Service, USDA.)

Corn rootworm control. For centuries, the agricultural management practices of Central American farmers prevented widespread outbreaks of the corn rootworm. Today's farmers in the Lake Atitlan area of Guatemala continue the practice of growing small plots of diverse, regularly rotated crops.

The corn earworm also feeds on cotton bolls. (Photograph by Keith Weller, courtesy of Agricultural Research Service, USDA.)