12.11: Production of Food and Fiber by the Biosphere - Agriculture

The most important use of soil and the biosphere for humans is agriculture, the production of food and fiber by growing crops and livestock. Agriculture is very closely tied with the practice of green chemistry in many ways. Agricultural chemicals, including fertilizers, herbicides, and insecticides are produced and applied to crops and land in enormous quantities. Annual production of millions of kilograms of these chemicals demands the proper practice of green chemistry and engineering. The judicious use of relatively small quantities of herbicides enables planting of crops in soil covered with residues of the previous year’s crops with little or no cultivation of soil. This practice of low-tillage agriculture, now called conservation tillage (see Section 11.11), is in keeping with the best practice of green chemistry and industrial ecology. Organic biomass produced by plants can be used as a renewable source of raw material and fuel. Some plants are now being genetically engineered to produce specific chemicals.

The practice of agriculture is absolutely essential for the survival of humankind. In order to continue to feed growing world populations while maintaining and even enhancing the ability of soil to produce food, it is necessary that the practice of agriculture be as green as possible. In the past and still today, this has often not been true. Cultivation of soil by humans has displaced native plants, destroyed wildlife habitat, contaminated soil with pesticides, filled rivers and bodies of water with sediments, and otherwise perturbed and damaged the environment. Agricultural practices arguably represent the greatest incursion of the anthrosphere into the other environmental spheres. On the positive side, growth of domestic crops temporarily removes greenhouse gas carbon dioxide from the atmosphere and provides organic raw materials and biomass fuel without any net addition of carbon dioxide to the atmosphere.

The basis of agriculture is the development of domestic plants from their wild ancestors. (The same can be said of animals, but only a handful of animal species have been domesticated, although each consists of many different breeds.) Our prehistoric ancestors learned to select plants with desired characteristics for the production of food and fiber, developing new species that often require the careful efforts of expert botanists to relate them to their wild ancestors. Only around 1900 were the scientific principles of heredity applied to plant breeding, eventually with excellent results. Using scientific methods, agriculturists accomplished a “green revolution” in the 1950s and 1960s that resulted in varieties of rice and wheat, especially, that had vastly increased yields. The techniques used included selective breeding, hybridization, cross-pollination, and back-crossing to develop grain varieties which, combined with chemical fertilizers and pesticides, lead to much higher crop yields. India, a country on the verge of starvation in the 1940s, increased its grain output by 50%. Developments such as higher yielding and faster maturing dwarf varieties of rice enabled better nutrition for an increasing world population, at least postponing the inevitable problems that will result from population growth. By breeding plants resistant to cold, drought, and insects, overall crop productivity has been further increased. Increased nutritional values for grain have been achieved, such as the development of corn varieties that have higher levels of lysine amino acid.

One of the major advances in plant breeding has been the development of hybrids produced by crossing true-breeding strains of plants. So-called “hybrid vigor” is well known, and many hybrids have vastly greater yields than their parent strains. Corn, a remarkably productive photosynthesizer, has proven most amenable to the production of hybrids, in part because of the separation of male flowers which grow on the tops of plants from female flowers attached to the budding corn ears. By planting rows of corn that alternate between two different strains and cutting the tassels from the tops of the plants that are to produce the corn seed, hybrid corn varieties are readily produced. More recently, techniques have been developed for growing hybrids of other kinds of plants.

There are, of course, many factors other than the genetic strains of plants that are involved in high crop productivity. The effects of weather have been mitigated by the development of crop varieties that resist heat, cold, and drought. The provision of water by artificial irrigation has greatly increased crop productivity and is essential for crop productivity in some regions, such as the vegetable-growing areas of California. Irrigation practices continue to become more efficient with the replacement of wasteful spray irrigators by systems that apply water directly to soil, or even directly to plant roots. Computerized control of irrigation can make it much more efficient. Environmentally, widespread use of herbicides has had some excellent benefits, along with some harmful effects, by enabling greater crop productivity with less tillage of land.