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Agriculture and Nutrient Cycles. Chapter 2.7. Agriculture and Nutrient Cycles. The seeds, leaves, flowers and fruits of plants all contain valuable nutrients. As crops are harvested, the valuable nutrients are removed from the soil.

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agriculture and nutrient cycles1
Agriculture and Nutrient Cycles
  • The seeds, leaves, flowers and fruits of plants all contain valuable nutrients.
  • As crops are harvested, the valuable nutrients are removed from the soil.
  • This diversion of nitrates and phosphate from the local cycles would soon deplete the soil unless the farmer replaced the missing nutrients.
slide3
There are many other elements/nutrients that plants need, other than carbon.
  • Plants also need nitrogen (N), phosphorus (P), and potassium (K)
  • As plants grow, they remove these nutrients from the soil.
  • FERTILIZERS are materials used to restore soil nutrients and increase production from land.
slide4
However, adding too much fertilizer is not always better. Extra, unused fertilizer can end up in streams and lakes.
fertilizer and ecosystems
Fertilizer and Ecosystems

Read the first paragraph of “Fertilizer and ecosystems” on page 70 (10 minutes)

Question

What can happen to organisms when too much fertilizer is used?

Answer:

  • Nutrients allow algae to grow rapidly (algal bloom)
  • Algae use oxygen
  • Algae die
  • Bacteria uses oxygen
  • oxygen levels drop
  • fish / other animals die
  • decomposer eat
  • bacteria population grows
  • Bacteria use more oxygen.
questions
Questions
  • Answer questions Page 71
  • #2,5
solutions to questions
SOLUTIONS TO QUESTIONS
  • Q2 – Explain how excess fertilizers might affect decomposing organisms.
  • ANSWER:
  • Excess fertilizers cause algae to grow, when they die decomposers feed and grow in number.
solutions to questions1
SOLUTIONS TO QUESTIONS
  • Q5 – Explain why not planting a crop and then ploughing in the fall might help a farmer restore nitrogen and phosphorus levels in the soil.
  • ANSWER:
  • During the year nutrients, including nitrogen and phosphorous, accumulate in the plants that grow. If the farmer ploughs these plants under in the fall, the nutrients will help enrich the soil. This is called “green manure.”
pesticides

PESTICIDES

CHAPTER 2.2 ( Case Study )

Scan figure 4

things to do
THINGS TO DO:
  • Read Chapter 2.2
  • Page 52-57
  • Fill in the worksheet
  • 40 MINUTES TO COMPLETE
  • Check answers before the end of class
answers to worksheet
ANSWERS TO WORKSHEET
  • QUESTION 1 – Define the following:
  • A) Pest – is an organism that people consider harmful or inconvenient
  • Examples:
  • Weeds, insects, fungi, and rodents
  • B) Pesticide – chemicals designed to kill pests
  • Examples: Raid , DDT
slide13
QUESTION 3 – What is the main difference between first generation and second generation pesticides?

1st Generation – natural chemicals

(Metallic based, ex. Lead, mercury and arsenic)

Not only did they kill insects, they were highly poisonous for people.

2nd Generation – made in Laboratory

DDT is a potent insecticide made in 1874.

  • At the time it was made people did not know it’s harmful effects
  • (Effects: carcinogenic, thinning of egg shells, birth defects, etc.)
  • Extra:
    • 2.3 million tonnes of DDT was used/year (peak usage was in 1962)
    • Today, there are 500 registered insecticides used in Canada
    • 75% of the banned insecticides are still used in 3rd World Countries
extra place in notes
Extra: Place in Notes

3rd Generation Modern Day Pesticides – Water Soluble

  • Because they are water soluble they will not stay in the body
  • They can be excreted through sweat and urine and are easily broken down in the soil.
  • Problems: need to be reapplied frequently because they break down so quickly, they are only effective for short periods of time, cost for reapplication.
slide16
QUESTION 5 – Clearly explain BIOAMPLIFICATION
  • Is the increasing concentration of a toxin, in the fatty tissue, as organisms consume each other.
  • Second generation (early pesticides) were fat-soluble which means they would stay in the body. For example: If a grassland ecosystem was sprayed with DDT, the fat-soluble pesticides would stay in the herbivores body, and the carnivores body, etc… As the chemical accumulates so does the toxic effect.
slide17
QUESTION 5 B) – Provide an example of how Bioamplification occurs
  • The concentration of fat-soluble pesticide increases as you move up the food chain.
  • Page 54, Figure 4 provides a good example
  • 1 part per Grasshopper 4 part per Shrew 12 parts per Owl
slide18
QUESTION 5 C) – What can be done to prevent Bioamplification?
  • Make pesticides that do not stay in the fat tissue
  • Make pesticides that can be extracted from your body thru urination.
6 clearly explain how pest become resistant to pesticides
#6. Clearly explain how pest become resistant to pesticides.

A number of pests won’t be affected by pesticides (ex 10% of a population). They reproduce and their offspring are resistant as well.

slide20
QUESTION 6 – Reflect and Answer Parts L-P on pages 56-57
  • L) Speculate about why the spruce budworm hasn’t been eliminated after 40 years of spraying?
  • Spruce budworms have become resistant to the pesticides available. If all of the pests are not wiped out in the first wave, the survivors can multiply in number.
slide21
M) Why wouldn’t biologists just use extremely high concentrations of insecticides to kill all of the spruce budworms?
  • Concentrations of pesticide sufficiently high to kill all the spruce budworms would also kill many other species, beneficial as well as harmful, insects as well as other organisms.
slide22
N) Identify groups who have benefited from the NB spraying program.
  • The loggers and lumber and paper-mill workers have benefited from the New Brunswick spraying program.
slide23
O) Identify groups of people who might have suffered as a result of the decision not to spray?
  • The loggers, lumber and paper-mill workers, and First Nations peoples depending on the forests for a livelihood, might have lost out as a result of the decision not to spray on Cape Breton Island.