Chemistry for Changing Times 12 th Edition Hill and Kolb Chapter 20 Chemistry on the Farm… and in the Garden…and on the Lawn John Singer Jackson Community College, Jackson, MI © 2010 Pearson Prentice Hall, Inc.

20/2 Green Plants: Sun-Powered Food-Making Machines Green plants contain chloroplasts. These organelles have the ability to convert solar energy into food energy. 6 CO H 2 O + solar energy → C 6 H 12 O O 2

© 2010 Pearson Prentice Hall, Inc. 20/3 Green Plants: Sun-Powered Food-Making Machines In an early agricultural society, people grew plants for food and obtained energy from food.

© 2010 Pearson Prentice Hall, Inc. 20/4 Green Plants: Sun-Powered Food-Making Machines Shown here is the flow of nutrients in a simplified system.

© 2010 Pearson Prentice Hall, Inc. 20/5 Farming with Chemicals: Fertilizers Fertilizers are used to replace plant nutrients that agricultural activities remove from the soil. There are three primary plant nutrients, nitrogen, potassium, and phosphorus.

© 2010 Pearson Prentice Hall, Inc. 20/6 Farming with Chemicals: Fertilizers Nitrogen Nitrogen from the atmosphere is unavailable for plant use. Legumes contain bacteria in root nodules capable of fixing nitrogen; lightning can also fix nitrogen. Anhydrous ammonia or nitrogen- containing fertilizers are also used to replace nitrogen removed from soil by crops.

© 2010 Pearson Prentice Hall, Inc. 20/7 Farming with Chemicals: Fertilizers Nitrogen

© 2010 Pearson Prentice Hall, Inc. 20/8 Farming with Chemicals: Fertilizers Phosphorus Phosphorus is used by plants in the phosphates of DNA and RNA as well as ATP. Animal bones and the ore, rock phosphate, are a source of phosphates that can be converted to fertilizer.

© 2010 Pearson Prentice Hall, Inc. 20/9 Farming with Chemicals: Fertilizers Potassium Potassium ions (K+) are taken up by the plants and used to balance fluids in cells. They are also involved in formation and transportation of carbohydrates and may be involved in protein synthesis. The most common form of potassium in commercial fertilizers in KCl.

© 2010 Pearson Prentice Hall, Inc. 20/10 Farming with Chemicals: Fertilizers Other Essential Elements In addition to the three major nutrients, three secondary plant nutrients, magnesium, calcium, and sulfur are needed in moderate amounts. Also, eight micronutrients are needed in smaller amounts.

© 2010 Pearson Prentice Hall, Inc. 20/11 Farming with Chemicals: Fertilizers

© 2010 Pearson Prentice Hall, Inc. 20/12 Farming with Chemicals: Fertilizers The “complete fertilizers” that are purchased by farmers and home gardeners usually only contain the three major plant nutrients. The numbers on the fertilizer bags/boxes, such as , give the percentage of N, P 2 O 5, and K 2 O, respectively.

© 2010 Pearson Prentice Hall, Inc. 20/13 The War Against Pests Insects have always been a problem involved with our food production. Insecticides are used to kill insects.

© 2010 Pearson Prentice Hall, Inc. 20/14 The War Against Pests DDT was developed shortly before World War II and was at one time considered to be an ideal insecticide. Its widespread use has saved many human lives from disease and at the same time has caused much environmental damage.

© 2010 Pearson Prentice Hall, Inc. 20/15 The War Against Pests DDT is a persistent chemical substance, meaning it does not break down in the environment. It is fat-soluble and concentrates in fatty tissues. It is biologically magnified and causes the disruption of calcium metabolism. Its use has been documented to cause the decline of fish- eating birds.

© 2010 Pearson Prentice Hall, Inc. 20/16 The War Against Pests Organic phosphorus insecticides have been developed that are less persistent than DDT. Most are more toxic to mammals than DDT. Malathion is less toxic than DDT.

© 2010 Pearson Prentice Hall, Inc. 20/17 The War Against Pests Carbomates are another family of insecticides. Most are narrow-spectrum insecticides that are only directed at one or a few insect pests. They break down easily in the environment and do not accumulate in fatty tissue.

© 2010 Pearson Prentice Hall, Inc. 20/18 Biological Insect Controls Parasitic, predatory organisms, microbes, or viruses can be used to destroy target insects. The release of sterile insects to ineffectively mate with wild insects can reduce a population. Pheromones can be used to attract and trap certain insects. Juvenile hormones have been approved by the EPA to control mosquitoes and fleas. They prevent the nonreproducing larvae stage from forming adults.

© 2010 Pearson Prentice Hall, Inc. 20/19 Herbicides and Defoliants Herbicides are used to kill weeds and defoliants cause leaves to fall off plants.

© 2010 Pearson Prentice Hall, Inc. 20/20 Herbicides and Defoliants 2,4-D and 2,4,5-T 2,4-D (2,4-dichlorophenoxyacetic acid) was introduced in It is an herbicide that is effective against newly emergent, broad-leafed plants. 2,4-D can be purchased in garden supply stores. 2,4,5-T (2,4,5-trichlorophenoxyacid) is a defoliant that is effective against woody plants. 2,4-D and 2,4,5-T were mixed as a product called Agent Orange, which was used in Vietnam to defoliate the jungle and kill crops of the enemy. Unfortunately, 2,4,5-T contained a contaminant called dioxin that lead to birth defects and potential cancers. The EPA banned 2,4,5-T in 1985.

© 2010 Pearson Prentice Hall, Inc. 20/21 Herbicides and Defoliants Atrazine and glyphosate are the most widely used herbicides in the U.S. Atrazine binds to protein in chloroplasts and shuts down photosynthesis. Atrazine is used on corn crops. Corn is resistant to atrazine. Glyphosate is a nonselective herbicide that is metabolized by soil bacteria. Therefore, other plants can be grown on the soil shortly after use. It is sold by the trade name Round-Up®.

© 2010 Pearson Prentice Hall, Inc. 20/22 Herbicides and Defoliants Paraquat is a preemergent herbicide that inhibits photosynthesis by accepting electrons that would be used to reduce carbon dioxide. It kills weeds before crop seedlings can emerge and it is rapidly broken down in the soil.

© 2010 Pearson Prentice Hall, Inc. 20/23 Sustainable Agriculture Conventional farming uses pesticides and fertilizers that have negative environmental consequences. Conventional farming is also energy intensive. Organic farming does not use synthetic fertilizers or pesticides. It provides lower yields than conventional farming, but is more labor intensive.

© 2010 Pearson Prentice Hall, Inc. 20/24 Some Malthusian Mathematics Thomas Robert Malthus stated, in 1830, that the human population increases faster than the food supply. Unless population growth is controlled, poverty and war will be limiting factors. Populations grow geometrically and the food supply grows arithmetically.

© 2010 Pearson Prentice Hall, Inc. 20/25 Some Malthusian Mathematics The irony is that in the developed world, food is abundant and obesity is a concern, while in the developing world, malnourishment is still a fact of life.

© 2010 Pearson Prentice Hall, Inc. 20/26 Can We Feed a Hungry World? Earth’s population continues to grow. Modern agriculture has greatly increased our food production. At some point, limiting factors will affect the human population. The only questions are when and how? We can reduce the birthrate and/or increase the deathrate through war, famine, pestilence, or destruction of our environment.