Chapter 15 Optimizing food production

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Chapter 15 Optimizing food production

• Golden rice two European scientists created a
  new strain of rice enriched in ß-carotene, which
  the body uses to make vitamin A. This is a kind
  of transgenic plant (?????).

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15.1 Humans eat at all trophic levels

• Only about 1 percent of the solar energy reaching
  the Earths surface is used in photosynthesis,
  producing 170 billion tons of organic material
  per year.
• Trophic structure (food chains)

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• No more than 10 percent of the energy contained
  in the organic material of one trophic level is
  incorporated into the next higher level.
• The higher the trophic level, the smaller the
  possible population of organisms.
• Eating meat is a luxury The amount of
  biochemical energy people will obtain from eating
  the chickens is minuscule compared with the
  amount of biochemical energy in raising the
  chickens. In the US, more than 70 percent of
  grain production is fed to livestock.
• If people in US ate 10 percents less meat, the
  savings in resources could feed 100 million
  people.

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15.2 Plants require nutrients
table15.1 essential elements for most plants
Element From available to plants Relative number of ions in dry plant material
Macronutrients
Nitrogen, N NO3-, NH4 1,000,000
Potassium, K K 250,000
Calcium, Ca Ca2 125,000
Magnesium, Mg Mg2 80,000
Phosphorus, P H2PO4-, HPO42- 60,000
Sulfur, S SO42- 30,000
Micronutrients
Chlorine, Cl Cl- 3000
Iron, Fe Fe3,Fe2 2000
Boron, B H2BO3- 2000
Manganese, Mn Mn2 1000
Zinc, Zn Zn2 300
Copper, Cu Cu, Cu2 100
Molybdenum, Mo MoO42- 1
Measured relative to molybdenum1 Source
Salisbury and ross, plant physiology. Belmont,
CA Wadsworth, 1985
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• Plants utilize nitrogen, phosphorus, and
  potassium
• Plants need nitrogen to build proteins and a
  variety of other biomolecules, such as
  chlorophyll (???).
• Nitrogen fixation

fig 15.4 two pathways for nitrogen fixation, a
source of nitrogen for plants. (a) both
free-living bacteria in the soil and
microorganisms in root nodules produce ammonium
ions. (b) lightning provides the energy needed to
form nitrate ions from atmospheric nitrogen.
nitrogenase
Soil bacteria
Root nodule
N28H6e-
2NH4
lightening
2NO3-
N23O22e-
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• Plants need phosphorus to build nucleic acids,
  phospholiqids, and ATP.
• Potassium ions activate many of the enzymes
  essential for photosynthesis and respiration.
• Plants also utilize calcium, magnesium, and
  sulfur
• Calcium ions are essential for building cell
  walls.
• Magnesium ions are essential for the formation of
  chlorophyll.

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15.3 Soil fertility is determined by soil
structure and nutrient retention

• Topsoil usually contains sand, silt, and clay.
• Fertile topsoil is a mixture of at least four
  components mineral particles, water, air,
  organic matter.

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Soil readily retains positively charged ions
Mineral particle
Positively charged nutrient ions
mineral
Plant root
humus
phenolate
Fig 15.10 the negatively charged surfaces of soil
mineral particles and humus help retain
positively charged nutrients
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• The pH value of soil is largely a function of
  carbon dioxide present. A healthy soil may have
  enough carbon dioxide as a product released from
  to give a pH value of 4-7.
• Hydronium ions are able to displace nutrient ions
  held to mineral particles and humus.

? CO2 Reacts with H2O, forming H2CO3
? H2CO3 reacts with H2O, forming HCO3- and H3O
? H3O displaces nutrient ion (K shown), which
is then available to root
? Root releases CO2
Soil particle
root
Fig15.11 by releasing carbon dioxide, a plant
guarantees a steady flow of nutrients from the
soil to its roots
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15.4 Natural and synthetic fertilizers help
restore soil fertility

• Natural occurring fertilizers are compost (??)
  and minerals.
• The natural occurring minerals are limited.
• In 1913, a German scientist, Fritz Haber,
  developed a process for producing ammonia from
  hydrogen and nitrogen.

Kilogram per hectare
Fig 15.13 between 1956 and 1972 world crop yields
grew in tandem with increases in the use of
nitrogen fertilizers
Year
N-P-K system
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15.5 Pesticides kill insects, weeds, and fungi

• Insecticides kill insects
• The most widely used insecticides are chlorinated
  hydrocarbons, organophosphorus compounds and
  carbamates.
• The chlorinated hydrocarbons have a remarkable
  persistence, killing insects for months and years
  on treated surface since they are not degradable
  and water soluble.
• DDT The early increased crop yields resulting
  from DDT use were not sustainable.

Fig 15.15 the chemical name for DDT is
dichlorodiphenytrichloroethane
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Silent Spring and bioaccumulation
Fig15.17 the DDT concentration in a food chain
can be magnified from 0.000003 parts per million
(ppm) as a pollutant in the water to 25 ppm in a
bird at the top of the chain
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Alternatives to DDT
methoxychlor
Polar products (water-soluble)
Fig 15.18 methoxychlor is one of many
alternatives to DDT, enzymes in the liver can
clean the ether groups to produce polar products.
Look back to Fig15.15, and you will see that DDT
lacks ether groups
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Phosphorous compounds and carbamates
Malathion (an organophosphorus compound)
Carbaryl A carbamate
Fig 15.20 the widely used pesticides malathion
and carbaryl
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Herbicides kill weeds
Fig 15.21 the herbicides 2,4-D and 2,4,5-Tand the
dioxin contaminant TCDD
Fig 15.22 the herbicides atrazine, paraquat, and
glyphosate
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Fungicides kill fungi
Fig 15.23 the fungicide thiram
thriam
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15.6 There is much to learn from past
agricultural practice

• Pesticides are toxic.
• Fertilizers damage the ecosystem. (Blue-baby
  syndrome caused by excessive amount of nitrate in
  water).
• Over-use of fertilizers also hardens the
  top-soil, which would be much easily to be
  removed.

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15.7 High agricultural yields can be sustained
with proper practice

• Organic farming is environmentally friendly
  (concern for environment and a commitment to
  using only chemicals that occur in nature)
• Crop rotation
• Compost
• Organic farming is energy effective.

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• Integrated crop management is a strategy for
  sustainable agriculture
• Multi-cropping
• Integrated pest management
• Pheromones (???)

Fig 15.34 female gypsy moths emit the pheromone
disparlure (top) to entice male gypsy moths
(bottom left) into mating. The males are so
sensitive to one molicule in 1017 molecules of
air. This astounding sensitivity enables them to
respond to a female who may be more than 1
kilometer away. However, they can also be tricked
into responding to insecticide traps laced with
synthetic disparlure (bottom right)
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• 15.8 A crop can be improved by inserting a gene
  from another species
• Transgenic organisms
• Bovine growth hormone (?????)
• 15.9 World hunger is not inevitable