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.
• This diversion of nitrates and
phosphate from the local cycles
would soon deplete the soil unless
the farmer replaced the missing
nutrients.
• 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.
• However, adding too much fertilizer
is not always better. Extra, unused
fertilizer can end up in streams and
lakes.
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:
1. Nutrients allow algae to grow rapidly
(algal bloom)
2. Algae die
3. Bacteria decompose algae so they increase.
4. Bacteria use up all the oxygen in the water.
5. Fish / other animals die
Fertilizer and Ecosystems
Q2 Why do the levels of nitrogen and
phosphorus in fields decline when crops
are harvested?
Answer:
Nitrogen and phosphorus along with
water are drawn up by the roots
of the plant so when crops are
harvested, hence removed – these
nutrients are removed with the
plant.
SOLUTIONS TO QUESTIONS
• Q3 – Explain how excess fertilizers
might affect decomposing organisms.
• ANSWER:
• Excess fertilizer can seep into
waterways and cause the growth of
algae. When the algae die, the
population of decomposers increases
rapidly, causing oxygen depletion in
the water.
SOLUTIONS TO QUESTIONS
• Q4 – 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
CHAPTER 2.2 ( Case Study )
Scan figure 4
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
• 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
•QUESTION 2 – Complete the table on
the advantages and disadvantages of
pesticide use:
Advantages
Disadvantages
Controls unwanted
populations
Pollution (Air and
Water)
Increases Food Yields
Bioamplification
Prevent diseases
Ecosystem Decline
(alternates)
Toxic on body
Bugs become
resistance
• 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
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.
•QUESTION 4 – Complete the table on
the types of pesticides:
Type of
Target
Persistence
Pesticide
Insecticide
Insects
2-15 years
Herbicide
Weeds
Days to
Weeks
Fungicide
Fungi/Moulds
Few Days
Bactericide
Bacteria
Few Days
Rodenticide
Rodents
Few Days
• 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.
• 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
• 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.
Pests that aren’t affected by
pesticides and are adapted to
live even if they come in contact
with a pesticide. They
reproduce and their offspring
are resistant as well.
• QUESTION 6 – Reflect and Answer
Parts L-P on pages 56-57
• L) 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.
• M) 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.
• N) The loggers and lumber and
paper-mill workers have benefited
from the New Brunswick spraying
program.
• O) The loggers, lumber and papermill 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.
• P) Not spraying on Cape Breton
Island has allowed the ecosystem
to adjust and naturally recover
from the spruce budworm
infestation.