Advanced Biology: Bahe & Deken. Agriculture & Nutrition. Chapter 9. Text Page

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1 Agriculture & Nutrition Chapter 9 Text Page

2 9.1 Strategy of Agriculture What does it take to put food on the table at your house? Think about this question in terms of economics, energy, and ecology. The major challenge of agriculture is to feed the world while preserving our biosphere. The first step in accomplishing this goal is to figure out the most efficient way to grow food. As the graph below shows, during ecological succession at first biomass increases the fastest and then over time levels off. Hence, the most efficient way to grow perennial plants and, thus, crops is in good sunlight on well-fertilized and watered open land. First, the seed bed is prepared. Then the crop is planted. Fertilizer and water are added. When the crop is ready, it is harvested. Unused parts of the plant are returned to the soil and the process repeats itself year after year. 9.2 Soil: Nonliving Link to the Living As you have learned earlier this semester (and at Bio Drey Land), terrestrial life is supported by soil. Without the essential nutrients that soil provides and without the proper composition of good soil there wouldn t be enough plant growth to feed animals and people. Ultimately, the key to a healthy ecosystem is good, rich soil. Soil is a mixture of minerals, organic matter, water, and air. It has a definite structure and composition, and forms on the surface of land. Many soils have three major layers: top soil, subsoil, and parent matter. These layers make up the soil profile. The soil profile represents the succession of distinctive soil layers from the surface down to the unchanged parent material beneath it. Total Biomass Time This method of farming has been highly successful in the developed world and is why most people eat so well. This success, however, has produced some problems. These include: 1) Plowing large areas increases the potential for soil erosion, 2) Planting areas with a single crop (monoculture) makes it easy for pests (diseases and insects) to find food sources, 3) Significant energy is required to produce food and fertilizer. We are mainly concerned here with the top soil since it is here that the living and nonliving link together to produce the food that supports all life on Earth. Top soil contains a mixture of organic and inorganic nutrients that make it valuable economically because it supports agricultural crops. High Text Page

3 quality top soil is usually dark brown, dark gray, or black because of the humus it contains. Humus is the highly decomposed plant and animal residue that makes up much of the organic nutrients composing the soil. Because of its texture, a good topsoil will hold adequate moisture and allow air to circulate, which are required for photosynthesis to take place. Decomposers break down humus to free the nitrates, phosphates, and sulfates that are required by plants. Fertile soils contain and are able to supply a complete set of nutrients required by growing plants. The major essential nutrient elements supplied through soil are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Other major nutrients like carbon, hydrogen, and oxygen come from water and the atmospheric carbon. Nitrogen, phosphorus, and potassium are of particular interest to farmers and other plant growers since plants require relatively large quantities of these elements. When plant materials are harvested over and over from the same area, the soils are quickly depleted of these elements. This is why the main components of fertilizers are nitrogen, phosphorus, and potassium. The nutritional needs of animals include water, oxygen, minerals, vitamins, proteins, carbohydrates, and fats. Water is needed to regulate body temperature, to move nutrients, to carry waste, to participate in metabolic reactions, and to carry watersoluble vitamins. Oxygen is required for respiration, which is the breakdown of food by organisms to release nutrients, energy, carbon dioxide, and water. Essential mineral nutrients are involved in the functions of nerves and muscles, the formation of bones and teeth, the activation of enzymes, and in the case of iron, the transport of oxygen. Vitamins are organic molecules that are needed in small quantities to perform specific biological functions (i.e., vitamin K is important for blood clotting). Proteins in food are broken down into amino acids that are reassembled to make body proteins. The breakdown of carbohydrates provides our body s main source of energy. Fats and oils help maintain cell membrane structure and function. Humans or animals need sufficient amounts of fats, protein, and carbohydrates, but if too much is taken in they are converted to body fat. 9.3 Animal Nutrition As we have learned animals get their food by eating green plants. Energy is acquired by breaking down the energy-rich products of photosynthesis into simpler molecules. Many of these less energetic molecules become the nutrients that the animal absorbs for the building of its own body parts. The chemical reactions that take place in an organism as food is used are referred to as metabolism. Nutrition is the uptake of materials necessary for metabolism. Text Page

4 Questions Name: 1. Why is farming an efficient way to grow crops? 2. Why is soil considered the nonliving link to the living? 3. Name 3 nutritional needs of animals and why these 3 nutrients are needed. Text Page

5 9.4 Food from Livestock Most of the plant crops produced in the United States provide more food energy than the energy used to grow them. However, if we include livestock as well as crops, total food production uses about three units of fossil fuel energy to produce one unit of food energy. If we were to consider the energy used to grow, store, process, package, transport, refrigerate, and cook all plant and animal food, an average of about 10 units of fossil fuel energy are needed to put 1 unit of food energy on the table. Only about 10% of the world s land is suitable for growing crops, whereas about 20% is suitable for grazing cattle and sheep. For thousands of years domesticated animals such as cattle, horses, oxen, sheep, chickens, and pigs have played important roles in the human economy by providing food, fertilizer, fuel, clothing, and transport. When both crops and livestock are grown on diversified farms, the livestock return nutrients to the soil as manure and provide power. During the past 50 years the global livestock population has exploded as increased affluence has led to rising production and consumption of meat. Currently about 1.5 billion people in developed countries live high on the food chain by having a diet based on high consumption of meat and meat-based products. As a result, the world s developed countries, with one-fifth of the world s population, use their affluence to consume more than half of the world s grain. An increasing amount of livestock production in developed countries is industrialized; large numbers of cattle are typically brought to crowded feedlots, where they are fattened up for about 4 months before they are slaughtered. Most pigs and chickens in developed countries spend their entire lives in densely populated pens and cages and are fed mostly grain grown on cropland. The meat-based diet of affluent people in developed countries has enormous effects on resource use, environmental degradation, pollution, and disease. More than half of the world s cropland is used to produce livestock feed grain. Livestock also use more than half of the water withdrawn each year in the United States; most of this water Text Page

6 irrigates crops fed to livestock and washes nutrient rich manure from crowded livestock pens away. About 14% of the U.S. topsoil loss is directly associated with livestock grazing leading to desertification, the conversion of productive nutrient laden land into desertlike land. Cattle belch out 12-15% of all the methane released into the atmosphere (methane production increases the likelihood of acid deposition and is a powerful greenhouse gas). 9.5 Genetic Engineering One way to improve food production is to improve crop yields. Many plant characteristics, including the size and sweetness of the edible portion, hardiness, drought resistance, rate of growth, tolerance to soil conditions, dependence of fertilizers, and pest resistance, are at least partially genetically determined. Therefore, improving plant genomes can increase the yield, both in terms of the amount of crop per hectare and the amount of nutrition per unit of crop. The possible goals of genetic improvement include the development of new crop plants such as drought-resistant strains, pest-resistant strains, or strains with diminished nutrient requirements, capable of growth on marginal or poor soils. The kinds of changes to a species that can be accomplished by traditional methods of selective breeding (also called artificial selection) are limited by the genetic variation that exists within the species or its close relatives. Genetic engineering offers a newer method for customizing food crops by giving them genetic traits that they normally lack. An estimated 70% of all soybeans and alfalfa grown in the United States is now genetically modified, along with a smaller percentage of corn (about 35%) of corn. See the previous page that shows the methods for inserting new genes into plant cells. The Union of Concerned Scientists has recently published a summary of their concerns with plant biotechnology. Their main concern is the possible escape of genetically altered strains as superweeds. Transgenic plants have the potential to cross-pollinate with weeds (many plant species including wheat frequently do crosspollinate with weeds of related species). This is particularly worrisome if herbicideresistant plants pass their transgenes (genes introduced from a separate species) to weeds, making the weeds herbicide resistant. Transgenic plants (meaning those with genes derived from another species) have been produced in over 20 species, including tomatoes, potatoes, carrots, alfalfa, corn, soybeans, peas, cotton, rice, and sugar beets. Text Page

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8 Questions 1. What is desertification and how is it accomplished? Name: 2. If the demand for imported food increases as projected, few African countries will be able to compete with more affluent Asian countries in a bidding contest for grain. Africa uses grain more efficiently by using it mostly for direct human consumption. Asians feed much of their food imports to livestock to supply a growing demand for meat and meat products as their affluence increases. a. Does Africa have a greater moral claim on surplus food than Asia because of its more efficient use of grain? Explain. b. Does the United States, with one of the world s highest levels of meat consumption, have a moral responsibility to cut its grain consumption to make more grain available for export to countries whose people get most of their food by direct consumption of grain? Explain. 3. Artificial selection and genetic engineering are both ways of modifying plants. In what ways are the two methods similar? In what ways are they different? Text Page