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.
Allowed an increase in the size of the human population.

4. Shifting Agriculture
Shifting agriculture – deforestation, cutting down, burning trees and other vegetation in a small forested area.
Burning releases nutrients bound up in biomass.
Cleared soil is useful for 2-3 years.
Forest eventually recolonizes the area but often slow recovery.
Particularly useful on thin tropical soils.
Not suitable for large, densely populated areas.
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:
Growing site does not allow mechanization.
Crop does not allow mechanization.
Economic condition does not allow purchase of mechanized equipment.

5. Labor-Intensive Agriculture
Economics - Primary driver of labor-intensive agriculture.
Many densely populated countries have numerous small farms that can be effectively managed with human labor.

6. Mechanized Monoculture Agriculture
Mechanized monoculture agriculture is typical of industrialized countries.
Fossil fuel replaces human muscle power.
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.
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.
5 metric tons of fossil fuel used to produce 1 metric ton of fertilizer.
Developed world is dependent on oil for energy to manufacture pesticides, fertilizer and run machines.
Price of oil controlling factor on world’s ability to feed itself.

7. Monoculture Concerns Mechanized monoculture agriculture -
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.

8. 14.2 Fertilizer and Agriculture
Approximately 25% of the world’s agriculture crop directly attributed to chemical fertilizer use.
Fertilizers replace soil nutrients extracted by plants.
The price and availability of chemical fertilizers strongly influenced by world’s energy prices.
Macronutrients - three primary soil nutrients - nitrogen, phosphorus, and potassium.
Micronutrients (e.g., boron, zinc, and manganese) are needed in smaller amounts.
Chemical fertilizers - do not replace soil organic matter, 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.

9. 14.3 Agricultural Chemical Use
Pesticide - any chemical used to kill or control populations of unwanted fungi, plants, or animals (pests).
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.

10. 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.

11. Insecticides
Insecticides are used to control insect populations – naturally occurring and chemically manufactured..
3,000 years ago, Homer noted the use of sulfur to control insects.
Naturally occurring - Certain plant products produce repellant chemicals.
Nicotine (tobacco)
Rotenone (tropical legumes)
Pyrethrum (chrysanthemums)
Synthetic Chemicals – development seen as 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.

12. Pesticides - Chlorinated Hydrocarbons
Chlorinated hydrocarbons - group of complex, stable-structure, long-lasting, persistent pesticides.
Effective for long periods after application.
Tend to accumulate in soil and animal bodies.
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.

13. Pesticides - 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.
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.

14. Herbicides
Herbicides - 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.
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

15. 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.
Monsanto Weed Killer Roundup Faces New Doubts on Safety in Unsealed Documents
By DANNY HAKIMMARCH 14, 2017

16. 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.
The dangers associated with the consumption of large amounts of methylmercury in fish are well recognized, and there is some evidence to suggest that methylmercury may be the cause of subtle neurological impairments when ingested at even low to moderate levels, particularly the prenatal and early childhood periods.
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.

17. 14.4 Problems with Pesticide Use
A perfect pesticide would have the following characteristics:
Inexpensive
Only affect target organisms
Short half-life (nonpersistent)
Break down into harmless materials
Newer pesticides improved over early pesticides, but all have problems.
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.
Bioaccumulation - 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 - 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.

18. The Biomagnification of DDT

19. 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.

20. 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.

21. 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.
WHO estimates between 1 million and 5 million acute pesticide poisonings occur annually, resulting in 20,000 deaths.
Most critical health problem is inadvertent exposure to small quantities for majority of people.
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.

22. 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.

23. 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.
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.

24. 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.

25. 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.

26. 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.
Precision agriculture - technique that addresses many of these concerns.
Use of computer technology and geographic information systems, it is possible to automatically vary the chemicals applied to the crop at different places within a field based on soil and topography.
Crop rotation - effective way to enhance soil fertility, reduce erosion, and control pests.

27. 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

28. 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

29. Biological Control of Purple Loosestrife

30. 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.

31. 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.