Physical Factors Affecting Crops Water

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Physical Factors Affecting Crops - Water
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Water

• Key physical factor
• Universal solvent for living systems
• More limiting than CO2

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Water as a physical factor follows similar
pattern as most physical factors
Water
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Water Optimum range often wider and flatter
than for most physical factors
Important in irrigation to avoid excess and waste
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Too much water? Raised beds avoid excessive water
levels
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Pigeonpea crop adapted to low water
requirements
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Familiar graph for most physical factors
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Ecological Niche

• Similar graphs could be drawn for most factors
  (food, water, light, space, temperature, etc.),
  defining limits and optimum ranges for each
  factor.
• Ecological niche for a species is defined by the
  combination of its requirements for every
  physical and biological resource (n dimensions).

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Ecological Niche Principles

• The niche requirement that is most limiting will
  determine growth rate or even presence of the
  organism.
• Law of the minimum (also applies to
  excesses!)
• 2. If niche requirements of two species are
  similar, they will compete, restricting one
  another.

How well do multiple crops/weeds share resources?
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Ecological Niche

• There can be a large difference between potential
  or fundamental niche (all adequate conditions for
  a species) and actual or realized niche that the
  organism actually occupies.

Actual niche
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Ecological Niche

• 4. Niche breadth is important for adaptation.

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Ecological Niche

• Organisms can share resources without competing.
  Niche partitioning of resources due to (see
  Price, 1997, pp. 569-576)
• a) character displacement (e.g., ant mandible
  size and seed size).
• b) habitat (e.g., latitudinal effects)
• c) microhabitat (smaller scale)
• d) time of day or season
• e) food and dietary differences

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Water Cycle Plant Level
Transpiration water loss through stomata of
plants
Rain or Irrigation
Water in Soil
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Water Cycle Plant Level
ET Evapotranspiration combined water loss
from unit of land evaporation plus transpiration
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Principles of ET and Water Movement

• Water vapor (and water) moves from areas of high
  concentration to low conc.
• Increased water on leaves reduced
  transpiration reduced ET

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ET potential of environment to evaporate water
affected by

• Solar radiation
• Temperature
• Relative humidity
• Soil type
• Wind
• Mulch

How would an increase in each of these factors
affect ET?
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ET potential of environment affected as we
increase

• Solar radiation increased evap transp
• Temperature increased evap transp
• Relative humidity reduced water movement
• Soil type depends affects water holding
  capacity
• Wind moves water vapor away, increased ET
• Mulch cover decreases evap

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Water Cycle Local and World Basis
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Critical Areas in Agroecosystem Water Cycle

• Soil moisture ability of soil to hold water
• Shortages balance between use for irrigation
  and recharge (water supply often comes from
  outside of ecosystem)

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Water Issues in Agriculture

• Quality Condition of incoming (rain, irrig.)
  vs. outgoing (runoff, percolation) water
• Quantity Irrigated ag a net user of water,
  can lead to groundwater depletion
• Soil moisture need to maintain during crop
  growth

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Irrigated Agriculture and Groundwater Depletion

• Future supply can run short reduced aquifers,
  increased well depths
• Salt water intrusion
• Subsidence

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Water Cycle Local and World Basis
Groundwater
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References

• Text, pp. 83-85.
• Odum, 1983. Ch. 4.
• Price, 1997. Ch. 20, pp. 553-557 569-576.
• Schlesinger, 1991. Ch. 10.
• Tivy, 1992. Ch. 3.