1. ENVIRONMENTAL SCIENCE
14th Edition
A Study of Interrelationships

2. Outline 14.1 The Development of Agriculture
14.2 Fertilizer and Agriculture
14.3 Agricultural Chemical Use
14.4 Problems with Pesticide Use
14.5 Why Are Pesticides So Widely Used?
14.6 Alternatives to Conventional Agriculture

3. 14.1 The Development of Agriculture
Development of agriculture involved manipulating the natural environment to produce food desired by humans.
This allowed an increase in the size of the human population.

4. Shifting Agriculture
Shifting agriculture involves cutting down and burning the trees and other vegetation in a small area of the forest.
Burning releases nutrients bound up in biomass.
The cleared soil is useful for 2-3 years.
Forest eventually recolonizes the area.
Particularly useful on thin tropical soils.
Not suitable for large, densely populated areas.
Requires a long recovery time between cycles.

5. Shifting Agriculture
Shifting agriculture often employs polyculture, or the planting of a mixture of plants.
Labor-intensive agriculture is practiced in much of the world.
Three situations favor this type of agriculture:
The growing site does not allow mechanization.
The crop does not allow mechanization.
The economic condition does not allow purchase of mechanized equipment.

6. Labor-Intensive Agriculture
The primary reason for the use of labor-intensive agriculture is economic.
Many densely populated countries have numerous small farms that can be effectively managed with human labor.

7. Mechanized Monoculture Agriculture
Mechanized monoculture agriculture is typical of industrialized countries.
Fossil fuel replaces human muscle power.
This method requires large amounts of energy and flat land.
Monocultures promote more efficient planting, cultivating, and harvesting.
Farmers often rely on hybrids to provide uniform monocultures.

8. Energy and Mechanized Agriculture
Labor reduction in the United States:
1913: 135 hours of labor required to produce 2,500 kg of corn.
1980: 15 hours of labor required to produce 2,500 kg of corn.
It takes 5 metric tons of fossil fuel to produce 1 metric ton of fertilizer.
The developed world is dependent on oil to produce energy to manufacture pesticides and fertilizer and to run machines.
The price of oil has wide ramifications on the world’s ability to feed itself.

9. Issues with Monoculture
Problems with mechanized monoculture agriculture include:
Large tracts of bare land increases soil erosion.
The planting of genetically identical seeds results in the loss of genetic diversity.
Little genetic differentiation often leads to increased pesticide use.
No crop rotation depletes soil nutrients, increasing fertilizer use.
Fossil fuel energy use has replaced human muscle power.

10. 14.2 Fertilizer and Agriculture
Approximately 25% of the world’s agriculture crop is directly attributed to chemical fertilizer use.
Fertilizers replace soil nutrients extracted by plants.
The price and availability of chemical fertilizers are strongly influenced by world’s energy prices.
The three primary soil nutrients (macronutrients) are nitrogen, phosphorus, and potassium.
Micronutrients (e.g., boron, zinc, and manganese) are needed in smaller amounts.

11. Increasing Fertilizer Use

12. 14.2 Fertilizer and Agriculture
Chemical fertilizers do not replace soil organic matter, which is important for soil structure.
Total dependency on chemical fertilizers usually reduces the amount of organic matter and can change the physical, chemical, and biological properties of the soil.

13. 14.3 Agricultural Chemical Use
A pesticide is any chemical used to kill or control populations of unwanted fungi, plants, or animals (pests).
Pesticides can be subdivided into several categories based on the organisms they control.
Insecticides control insect populations.
Fungicides control fungal pests.
Rodenticides control mice and rats.
Herbicides control plant pests.
Biocides kill a large variety of organisms.

14. 14.3 Agricultural Chemical Use
Pests are often referred to as target organisms.
Many pesticides kill non-target organisms as an unwanted side effect.
Persistent pesticides remain active for long periods.
Nonpersistent pesticides break down quickly.

15. Insecticides Insecticides are used to control insect populations.
3,000 years ago, Homer noted the use of sulfur to control insects.
It has been known for centuries that certain plant products produce repellant chemicals.
Nicotine (tobacco)
Rotenone (tropical legumes)
Pyrethrum (chrysanthemums)

16. Insecticides
The discovery of chemicals that could kill insects was celebrated as a major advance in the control of disease and the protection of crops.
Mosquitoes are known to carry over 30 diseases harmful to humans.
In 1867, the first synthetic inorganic insecticide was formulated.
In 1942, DDT became the first synthetic organic insecticide produced.
Several new categories of these compounds have since been developed.

17. Chlorinated Hydrocarbons
Chlorinated hydrocarbons are a group of complex, stable-structure, long-lasting, persistent pesticides.
They remain effective for long periods after application.
They tend to accumulate in soil and animal bodies.
They affect many non-target organisms.
They are no longer used in many parts of the world.
They are still used in many developing countries to protect crops and public health.
Because of their persistence and continued use in many parts of the world, they remain present in the food chain.

18. Organophosphates and Carbamates
Organophosphates and carbamates are short-lived pesticides that do not persist in the environment.
Both work by interfering with the ability of the nervous system to conduct impulses normally.
These pesticides affect the nerve cells of humans and other vertebrates as well.
Persons who apply such pesticides must use special equipment and should receive special training in safe application practices.

19. 14.3 Agricultural Chemical Use
Common organophosphates are malathion, parathion, and diazinon, which is widely used in gardens.
Carbaryl, propoxur, and aldicarb are examples of carbamates.
Carbaryl is sold under the brand name Sevin and is widely used in home gardens.

20. 14.3 Agricultural Chemical Use
Herbicides are used to control unwanted plants and are heavily used in genetically modified crops.
About 60% of pesticides used in U.S. are herbicides.
Weeds compete with crops for soil nutrients.
Traditional weed control methods are expensive in terms of time and energy.

21. Herbicides Several major types of herbicides are in current use.
Synthetic plant growth regulators mimic natural growth regulators (auxins).
2,4-D; 2,4,5-T
Photosynthetic disruptors
Enzyme inhibitors

22. Herbicides
Some herbicides are toxic to all plants (nonselective), and some are selective as to the plant species they affect.
Atrazine is often used to control broad-leaf and grassy weeds.
Glyphosate (Roundup) is a broad-spectrum, nonselective, systemic herbicide used to control annual and perennial plants.

23. Fungicides and Rodenticides
Fungicides are used to protect agricultural crops from spoilage, to prevent the spread of disease, and to protect seeds from rotting in the ground before they can germinate.
Methylmercury is extremely toxic to humans.
In some parts of the world, governments pay a bounty to people who kill rats because they can destroy agricultural crops.
Rodents also carry diseases harmful to humans.
Rodenticides must be used with great care to prevent poisoning non-target organisms.

24. 14.4 Problems with Pesticide Use
A perfect pesticide would have the following characteristics:
Inexpensive
Only affect target organisms
Short half-life
Break down into harmless materials
Newer pesticides have fewer drawbacks than early pesticides, but none are devoid of problems.

25. Persistence
Persistent pesticides become attached to small soil particles and are easily moved by wind or water.
They may be distributed throughout the world from local applications.
Persistent pesticides have been discovered in polar ice and are present in detectable amounts in the bodies of animals, including humans, throughout the world.

26. Bioaccumulation and Biomagnification
Bioaccumulation is the process of accumulating higher and higher amounts of material within an organism’s body.
Many persistent pesticides are fat soluble and build up in fat tissues.
Biomagnification is the process of acquiring increasing levels of a substance in bodies of higher trophic-level organisms.
DDT, mercury, and PCBs are all known to accumulate in ecosystems.
DDT was banned in the U.S. in the early 1970s.

27. The Biomagnification of DDT

28. Pesticide Resistance
Pesticide resistance is a problem associated with the widespread use of pesticides.
Insecticides only kill susceptible individuals.
Most surviving individuals have characteristics that allowed them to tolerate the pesticide.
Survivors pass on genetic characteristics for tolerance.
Subsequent pesticide applications become less effective.

29. Effects on Nontarget Organisms
Most pesticides are not species-specific, and kill beneficial species as well as pest species.
Many kill predator and parasitic insects that normally control pest insects.
Insecticides may change the population structure of the species present so that a species not previously a problem may become a serious pest.

30. Human Health Concerns
Short-term and long-term health effects to persons applying pesticides and the public that consumes pesticide residues in food are also concerns.
Acute poisoning during application sometimes occurs when farmers cannot read caution labels on packaging or do not have access to protective gear.
The WHO estimates between 1 million and 5 million acute pesticide poisonings occur annually, resulting in 20,000 deaths.

31. Human Health Concerns
For most people, the most critical health problem is inadvertent exposure to small quantities.
Farmers who were occupationally exposed to pesticides over many years show that they have higher levels of certain kinds of cancers than the general public.
Chronic minute exposures to pesticide residues in food or through contaminated environments are also of concern.

32. 14.5 Why Are Pesticides So Widely Used?
Food Production
Worldwide, pests destroy 35% of crops.
Economic Concerns
Pesticides increase yields and profits.
Health Reasons
Insecticides curtail many diseases.

33. 14.6 Alternatives to Conventional Agriculture
Prior to the invention of synthetic fertilizers and other agrochemicals,
Animal manure and crop rotation provided soil nutrients.
A mixture of crops prevented regular pest problems.
Manual labor killed insects and weeds.

34. 14.6 Alternatives to Conventional Agriculture
With the development of mechanization, many farmers changed from mixed agriculture to monocultures.
This presented greater opportunities for pest problems to develop.
Chemical pesticides were used to “solve” the problem.

35. 14.6 Alternatives to Conventional Agriculture
Alternative agriculture includes all nontraditional agricultural methods.
Sustainable agriculture seeks to produce adequate, safe food supplies in an economically viable manner while protecting or enhancing ecosystem health.
Organic agriculture is distinguished by methods that do not involve the use of artificial fertilizers, chemical growth regulators, antibiotics, pesticides, and genetically modified organisms.

36. 14.6 Alternatives to Conventional Agriculture
A sustainable approach to agriculture is characterized by several broad goals:
Keeping insecticide, herbicide, fungicide, and fertilizer use to a minimum.
Conserving soil and water resources.
Staying economically viable.
Encouraging biological diversity.
Healthy, biologically active soils lead to healthier, more insect- and disease-resistant plants and animals.
Natural or supplemented populations of beneficial insects (“good bugs”) will keep pests (“bad bugs”) below economically damaging levels.

37. Techniques for Protecting Soil and Water Resources
Changes in agricultural production methods can help to reduce the problems of soil compaction and loss of organic matter:
Reducing the number of trips farm equipment must make over the land reduces soil compaction.
Incorporating crop residue into the soil builds organic matter.
Reducing fertilizer runoff helps aquatic ecosystems.
Careful selection, timing, and use of pesticides decreases the extent to which these materials become environmental contaminants.

38. Techniques for Protecting Soil and Water Resources
Precision agriculture is a new technique that addresses many of these concerns.
With modern computer technology and geographic information systems, it is possible, based on soil and topography, to automatically vary the chemicals applied to the crop at different places within a field.
Crop rotation is an effective way to enhance soil fertility, reduce erosion, and control pests.

39. Integrated Pest Management
Integrated pest management (IPM) uses a variety of methods to control pests rather than relying solely on pesticides.
It requires information about:
Crop plant metabolism
Biological interactions between pests and their predators and/or parasites
Climatic conditions favoring pests
Techniques to encourage beneficial insects

40. Integrated Pest Management
Several methods are employed in IPM:
Disrupting reproduction
Female pheromones
Male sterilization
Natural predators
Aphids can be controlled with ladybugs
Bacterial strains

41. Insect Control with Natural Predators

42. Biological Control of Purple Loosestrife

43. Genetically Modified Crops
Developing resistant crops
Genetic engineering or biotechnology involves inserting specific pieces of DNA into the genetic makeup of organisms.
Genetically modified organisms can be developed for pest and herbicide resistance, although some groups are opposed to the use of genetically modified organisms.

44. Economic and Social Aspects of Sustainable Agriculture
Modifying farming practices
Crop rotation tends to prevent the buildup of specific pests that typically occurs when the same crop is raised in a field year after year.
Selective use of pesticides
Identification of the precise time when pesticide application will have the greatest effect at the lowest possible dose is a useful practice.

45. Summary
Most of the food in the world is raised on mechanized farms that use energy rather than human muscle for tilling, planting, and harvesting crops, and for producing and applying fertilizers and pesticides.
Mechanized monoculture depends heavily on the control of pests by chemical means.
Persistent pesticides are stable and persist in the environment, where they may biomagnify in ecosystems.
Most nonpersistent pesticides are more toxic to humans and must be handled with great care.

46. Summary
Pesticides can be divided into several categories based on the organisms they control.
Because of the problems of persistence and biomagnification, people are seeking pesticide-free alternatives to raising food.
Several different philosophies that seek the same ends—less use of chemicals and better stewardship of the soil—are alternative agriculture, sustainable agriculture, and organic agriculture.

47. Summary
One ingredient in all of these approaches is the use of integrated pest management, which employs a complete understanding of an organism’s ecology to develop pest-control strategies that use no or few pesticides.