Botkin and Keller Environmental Science 5e Chapter 12 Effects of Agriculture on the Environment.

Botkin and KellerEnvironmental Science 5e

Chapter 12

Effects of Agriculture on the Environment


Case Study: Clean-Water Farms

• Management practices adopted by a Kansas farmer reduced erosion and runoff of chemicals by converting acreage to grassland

• Intensive rotational grazing or management-intensive grazing involves rotating the animals among paddocks (fenced grazing areas) to disperse the waste and the allow the forage grass in idle paddocks to rejuvenate

• Higher quality, lower prices for consumer


Many environmental problems result from agriculture:

• Soil erosion • Sediment transport

and deposition downstream

• On-site pollution from fertilizers and pesticides

• Deforestation

• Desertification• Degradation of water

aquifers• Salinization• Accumulation of toxic

metals and organic compounds

• Loss of biodiversity


Reducing Soil Erosion

• Why does the soil erode?• wind-rows to break the wind• contour plowing to reduce erosion by water• no-till agriculture substitutes herbicides as a

means of controlling weeds – plowing is done in order to remove weeds that would

otherwise compete with the crop.

– soil is especially vulnerable to erosion between plowing and crop is establishment (WHY?)



A Closer Look: Soils

• Be able to describe the horizons (O,B,C, etc.) and how they differ

• There are many different types of soils. In general, temperate soils have a larger store of nutrients than tropical soils. This is due to the speed of decomposition (warm moist=fast). This influences the kind of agriculture that can be successfully practiced. In the tropics, most of the roots are directly on the soil surface where the leaves decay.

• Soil is composed of organic and mineral parts. The mineral part includes sand, silt and clay. These names refer to particle sizes. Sand is the largest, clay the smallest.


Where Eroded Soil Goes: Sediments Also Cause Environmental Problems

Ways to slow erosion:

• Making Soil Sustainable

• Contour Plowing

• No-Till Agriculture– Combination of farming practices that include

not plowing the land and using herbicides to keep down weeds.


Problems with Soil Erosion

• Eroded soil is transported, usually to rivers and lakes. U.S. rivers carry about 3.6 billion metric tons of sediment per year, 75% of it from agriculture land

• represents a loss of soil fertility, also has serious negative impacts on aquatic ecosystems, leading to eutrophication, killing benthic fauna and flora, and filling reservoirs.

• Soils and agriculture can be sustainable. However, it is important to make a distinction between sustainable crop production and a sustainable agricultural ecosystem. The former may require inputs of chemicals and energy from elsewhere, whereas the latter does not.



Integrated Pest Management

– Pests are any undesirable competitor, parasite or predator (herbivore)

– Control of agricultural pests using several methods together, including biological and chemical agents

– Goals:• To minimize the use of artificial chemicals

• To prevent or slow the buildup of resistance by pests to chemical pesticides


History of Pesticides

• The first stage in the technology was one of improvisation involving the use of fire, herbs, and poisons such as arsenic.

• A second stage starting in the 1930s ushered in the use of petroleum-based chemical sprays that were based on natural plant toxins. For example, nicotine is an excellent insecticide. These toxic chemicals, called botanicals, are produced by many plant species as defenses against herbivores.

• The third stage, the development of synthetic chemical pesticides. • The fourth stage takes advantage of deep knowledge about the biology

of pests to discover and exploit their weaknesses, such as the use of biological control agents (fighting fire with fire). The bacterium Bacillus thuringiensis (known as BT) is a good example of a natural disease organism that affects insect larvae and that can now be purchased as spores for use in the garden. There many other biological controls available and strategies, such as the use of sterile males to end an invasion by a founder population.


A Closer Look: DDT• Insecticide developed in the 1940s. • DDT belongs to a class of insecticides known as the chlorinated hydrocarbons.

It is a broad spectrum insecticide, it has a long half life (a decade or more), and concentrates in the food chain (biomagnification).

• Culminated in near extinction of predatory birds, alarming concentrations of DDT in human tissue and milk, and a book (Silent Spring, 1962, Rachael Carson).

• In January 1971, EPA issued notices of intent to cancel all Federal registrations of products containing DDT.

• During the 30 years prior to its cancellation, a total of approximately 1,350,000,000 pounds of DDT was used domestically.

• DDT concentrates in fat tissue, and by this mechanism it travels up the food chain becomes more concentrated. BIOMAGNIFICATION

• Since its ban, DDT continued to be manufactured in the U.S. for export to developing countries.

• 2001, the United States signed the Convention on Persistent Organic Pollutants (POPs) that commits the signatories to reduce and/or eliminate the production, use, and/or release of the 12 POPs of greatest concern to the global community, including DDT.


Integrated Pest Management• holistic pest management strategy combines biological control

and crop management with the limited and judicious use of chemicals.

• 700 million lbs of pesticides are used in the U.S. annually, about 80% of pesticide use is in developing countries.

• residues of this DDT, and/or its metabolites were found in approximately 5.6% of all vegetable and fruit samples tested in 1993 by the EPA

• Pesticides can be transported long distances. Pesticide residues can be found in Arctic and Antarctic ice. Herbicides account for about 60% of the pesticides in the nation’s waters. The effects are not fully understood. Pesticides that once were considered completely non-toxic to vertebrate animals (e.g. malathion) are now suspected as having reproductive side-effects (acting as xenoestrogens).


Integrated Pest Management• Biological controls

– No till, low till (predators live in soil)– Introduce natural predators

• Chemical pesticides– Limited application (up to 75% less)

• Planting methods – No monocultures, move away from planting in rows

• Control rather than eliminate. • Different methods of control for different pests


Integrated Pest Management


Genetically Modified Crops

• Faster and more efficient hybrids– Generally benign (very similar to what is already in existence)– Worry about super hybrids

• Terminator gene– Seeds are sterile– Can’t reproduce at will– But… Farmers must buy new seeds every year

• Transfer of genetic properties from different types of life. – Potentially most dangerous. – BT affects caterpillars and insect larvae, introduced into corn and

potato plants, spread out from pollen and landed on milkweed, ingested by monarch butterflies


Problems with GMC


Grazing on Rangelands

• Overgrazing occurs when the carrying capacity is exceeded. It can cause severe damage to lands

• It is important to properly manage livestock, including using appropriate lands for gazing and keeping livestock at a sustainable density

• Waste generated by livestock can impact aquatic ecosystems


Desertification

• Desertification is the deterioration of land in arid, semi- arid and dry sub humid areas due to changes in climate and human activities

• Desertification occurs when grazing or cultivation removes the native vegetation, leaving the soil vulnerable to wind erosion. The wind carries the small soil particles away, leaving sand. Sand is very permeable and holds little water, and this leads to desert-like conditions.

• Can be caused by– Poor farming practices– Conversion of marginal grazing lands to croplands

• About 1/3 of the Earth’s surface should be desert, based on climate, but 43% is desert, most of it in poor countries


Does farming change the biosphere?

• Agriculture changes land cover (reflection of light, evaporation, roughness, chemical exchange rates)

• Increases CO2 (fossil fuel use - CO2 released; clearing land speeds decomposition)

• Clearing land by fire releases particulates into atmosphere

• Fertilizer releases nitrogen, changing geochemical cycles

• Lowers species diversity.


Should rice be grown in a dry climate?

• The issue concerns the appropriate use of water in arid regions, but regional issues such as the importance of the fields to migratory birds complicate the issue.

• If human population were to double, what would be the additional environmental impacts of agriculture?

Botkin and Keller Environmental Science 5e Chapter 12 Effects of Agriculture on the Environment.

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