Chapter 12

Effects of Agriculture on the Environment

“Clean Water Farms”Case Study

• Intensive rotational grazing: is a system of grazing in which ruminant (animals that chew their cud) and non-ruminant herds are regularly and systematically moved to fresh pasture with the intent to maximize the quality and quantity of forage growth.

• The herds graze one portion of pasture, or a paddock, while allowing the others to recover.

• The grazers obtain the majority of their nutritional needs without the supplemental feed sources that are required in continuous grazing systems.

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

The American Dust Bowl of the 1930s

• Farming easily damages soils• Intensive plowing and major drought loosened the soil• The soil blew away during wind storms• Houses, cars, and farms were destroyed• Many farmers abandoned their farms • The Grapes of Wrath was first a novel made into a popular

movie about the dust bowl

Dust Bowl Video

Must Know This!

OnAlmost

Every

Birthday

Cupcakes

Rule

Click Here for Info

Where Eroded Soil Goes: Sediments Also Cause Environmental Problems

• Lots of soil is in water runoff that ends up in streams & rivers and then deposits it at the mouths of the rivers.

• These deposits end of destroying some fisheries• Coral reefs are also being destroyed by sediments

landing on them Click Here for Info

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.

Click Here for Info

Controlling Pests

• Pests in agriculture feed on the live parts of plants

• Include worms (nematodes), bacteria, viruses, weeds, vertebrates (mainly rodents & birds), and insects

• There are about 30,000 weeds (undesirable plants)

Pesticides

• Narrow Spectrum Pesticide: has a single target, just one pest, and not affecting anything else.

• Nice idea, but if a chemical is toxic to one it is very likely that it will be toxic to others….duh

• Arsenic was used which was very effective in killing pests and all other living things like humans

• Use of natural plant chemicals like nicotine but not as effective

• Use of artificial organic chemicals like DDT

DDT

• dichlorodiphenyltrichloroethane • Very effective but very toxic to especially apex birds• The WHO's (World Health Organization) anti-malaria campaign of the

1950s and 1960s relied heavily on DDT and initially the results were promising, though short lived.

• Resistance of mosquitoes to DDT was largely fueled by its often unrestricted use in agriculture.

• Once the mainstay of anti-malaria campaigns, as of 2008 only 12 countries were still using DDT, including India and some southern African states

• Rachel Carson’s the Silent Spring shed light on the use of DDT and its affect on the environment

Pest Control

• Biological Control: the use of biological predators and parasites to control pests

• Bacillus thuringiensis (BT) a bacterium which affects caterpillars and larvae of insect pests. Controls gypsy moths. This bacteria is harmless to humans and other mammals

• Small wasps: parasite on caterpillars• Ladybugs: predators of many pests• Sex pheromones: attract members of opposite sex

to insect traps and confuses mating patterns

Ladybugs and Praying Mantis

The goal of IPM (Integrated Pest Management) is to reduce the use of artificial pesticides, reduce costs & efficiently control

pests.Click for Info

Integrated Pest Management

– 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

Why Genetically Modified Crops?

1) Faster & more efficient hybrids.

2) “terminator gene”

3) Transfer a variety of traits.

Hybrids

• Genetically engineered hybrids are created to increase productivity and be pest resistant

• Could allow them to require less water • Attempts are underway to transfer the ability of having a

symbiotic relationship with bacteria to fix nitrogen• Problems:

– “Superhybrids” can grow where they are not wanted and become a pest

– Could create “superweeds” if a hybrid interbreeds with nearby weeds and transfer their new “super-powers”

– May require much more fertilizers, pesticides, and water leading to greater pollution & need for irrigation

Genetically Modified (GM) Crops

How can the genetic

characteristics of a GM crop

spread?

The Terminator Gene

• A genetically modified crop which has a gene to cause the plant to become sterile after the first year.

• Prevents GM crops from spreading.• Problem: more expensive, and developing countries are

less likely able to obtain these seeds…and farmers use seeds from first crop to plant the next crop…more expensive

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.

Desertification• Desertification is the deterioration of land in arid,

semi- arid and dry sub humid areas due to changes in climate and human activities

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

Symptoms of Desertification

• Lowering of the water table (wells have to be dug deeper and deeper)

• Increase in the salt content of the soil• Reduced surface water (streams and ponds dry up)• Increased soil erosion (the dry soil, losing its organic

matter, begins to be blown and washed away)• Loss of native vegetation (not having adapted to

desert conditions, native vegetation can no longer survive).

Preventing Desertification

• Monitor aquifers (underground water) & soil• Observe undesirable changes• Use proper methods of soil conservation, forest

management, and irrigation • Use of windbreaks (narrow lines of trees to help slow the

wind)• Reforestation over all, including planting windbreaks

Carrying capacity of pasture and rangeland in the US, in average number of cows per square kilometer.

Fighting Desertification