Importance of water

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Importance of water

• 90 of the plants weight
• The one most limiting factor in plant growth
• All transport of minerals and food is through a
  water medium
• Photosynthesis uses water
• Plant actually uses only 1 of the water absorbed

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Leaf curling in corn - protection against water
loss
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Spaces for Gas and Water

• Partical size effects spaces for gases and water.
• Water movement is dependent on the spaces

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• Adhesion and cohesive forces
• This is called capillary water

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Soil Water Availability

• Maximum retentive capacity (after rain)
• Gravitational water
• Field capacity (after loss of gravitational
  water)
• Capillary water
• Capillary movement in soil
• When gone, plant reaches permanent wilting point
• Hygroscopic water

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• Field capacity vs. gravitational water
• Hygroscopic water vs. available water

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Water Potential Soil Type
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Water movement in different soils
Distance from center of furrow
Sandy Loam
Clay Loam
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Perched water table

• Water accumulates because of impervious layer
• Often occurs with container grown plants
• Pore spaces at bottom of pot are filled with
  water
• Shallow pots have less growing room
• Growing medium should allow complete drainage
• Drainage holes in pot should be open

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Zones of Water use

• Upper quarter - 40
• 2nd quarter - 30
• 3rd quarter - 20
• 4th quarter - 10
• Upper quarter water critical for maximum
  transpiration growth

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Soil Water Loss

• Drainage (soil type has big effect)
• Transpiration
• Evaporation from surface
• Dependent on leaf area index
• Atmospheric vapor pressure
• Ways to conserve
• Mulch
• Weeding

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Irrigation
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Surface Irrigation

• Flood
• Furrow
• Border (or levee)
• Efficiency of water use may reach 60 in best
  circumstances

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Flood Irrigation

• Land should be graded (mostly level)
• Control structures or siphons for distribution
• Less power evaporation than sprinklers
• Distribution system inefficient

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Furrow vs. Sheet

• Furrow
• Delivers water well
• Most widely used for row crops
• Labor intensive
• Sheet (flood or levee)
• Crops like cranberries, orchards contained in
  levees
• Crops that can handle excess water

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Sprinkler Irrigation

• Even controlled application rate
• Slower rate of application (protects soil)
• Can be used on steep slopes
• Dont lose much land
• High initial cost
• Energy cost high
• Wind is biggest problem
• Water use efficiency approaches 75

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Subsurface

• Create artificial water table
• Ground must be level
• Soil subsurface must be permeable
• Bottom barrier needed

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Drip or Trickle Irrigation

• Delivered to individual plants
• Applied very frequently in small amounts
• Water pressure can be low
• Can be automated
• Helps overcome salt buildup
• Water not wasted between rows
• Can be used on high slopes

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Nile Delta
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Nile Delta
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Drip Irrigation Problems

• Soil particles can block emitters
• Ants can cut through lines
• Small mammals
• Bacterial slime build up in tubing

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Calculation of need

• Depends on evaporation and transpiration
• Overwatering can cause water logging
• Consider irrigation efficiency
• Best applied when 60 of available water is
  depleted

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