Irrigation

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Irrigation
By Keith Underwood Visiting Faculty Spring Qtr
2004
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Irrigation

• Providing plants and animals with resource based
  (stored) water in times when natural rainfall
  does not meet the needs for plant growth and
  field maintenance

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How to know when to Irrigate

• Monitoring Soil Moisture
• Weather conditions
• Plant needs new and verses established

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Monitoring Soil Moisture

• Soil Characteristics
• Crop Characteristics
• Available and Useable Soil Water

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Soil Components (mineral)

•  Very coarse sand  1.0 to 2.0 mm  
• Coarse sand  0.5 to 1.0 mm  
• Medium sand  0.25 to 0.5 mm  
• Fine sand  0.1 to 0.25 mm  
• Very fine sand  0.05 to 0.1 mm  
• Silt  0.002 to 0.05 mm  
• Clay  less than 0.002 mm

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Organic Matter as part of Soils

• There are 3 main components of organic matter in
  soils
• dead forms of organic material - mostly dead
  plant parts
• living parts of plants - mostly roots
• living microbes and soil animals

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Soil types
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Soil Depth Issues / Water Capacity

• Soil Layering
• Bedrock / Hardpan
• issues

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Soil Moisture Issues

• Soil Water Tension
• Field Capacity
• Permanent Wilting Point
• Plant available water holding capacity

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Soil Water Tension

• The ability of Soil to hold water in its
  structure
• Exercise

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Field Capacity

• The point where the soils ability to hold soil
  exceeds gravitys pull
• Tools

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Permanent Wilting Point

• Is the point where a plant is unable to exert
  enough energy to extract sufficient water from
  the soil to meet its needs.

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Plant available water holding capacity

• The difference between field capacity and
  permanent wilting point

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Crop Rooting Depth

 
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Tools and techniques for Soil Water Monitoring
and Measurement

• Soil feel and appearance
• Gravimetric sampling
• Tension meters

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Sampling

• Routinely done on a regular schedule to determine
  water needs.

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Soil Sampling

• The only true way to know the soil to water ratio
• Pw (wet sample weight-dry sample weight)/dry
  sample weight x 100

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Gravimetric Sampling

•  

 
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Tensiometer Sampling
 
Water filled tubes that have hollow ceramic tubes
that allow for soil / water tension to become
visible
 
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Break10 minutes
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The water system

• Manual above and below ground segments
• Automatic Above and below ground segments

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Manual System

• Controlled by owner/hired help
• More Flexible
• Generally less expensive

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Automatic Systems

• Ability to accurately time water applications
• Multiple zones are preset for watering
• Set schedule for water applications
• Generally more expensive
• Less labor cost after installation

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Types of Water Emitters

• Spray Sprinkler heads
• Rotary sprinkler heads
• Low flow emitters
• Bubblers
• Drip and micro-spray
• T-tape (measured space tubing with emitters laser
  cut into the pipe)

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Field Layout Considerations

• Size of field
• Location of mainlines (how to determine?)
• Availability of Water (source and volume)
• Time
• Type of system desired (considerations)

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Greenhouse

• Generally low pressure type systems
• Layout determined by Greenhouse planting plan

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Open Field

• Row or beds
• Low flow or high pressure systems
• Crops grown and pest issues
• SLOPE of field (very important!)

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Irrigation Design Considerations

• Determine amount of coverage desired
• Evaluate water supply availability
• Determine number of hours or period for
  irrigation (the schedule)
• Determine how much water is needed
• Select appropriate irrigation system type
• Determine control and sequence settings

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How to know?

• Most farm land purchased is already developed and
  has existing systems in place.
• How do we find out about the system and know its
  meets the needs?

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Question?

• What is the capacity of the Organic Farms
  Irrigation system?
• Lets find out.

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Class ExerciseItems needed includea watch
with second handa bucketTurning on the system,
time the amount of time it takes to fill the
bucket from one sprinkler. Add total amount of
water collected to determine the gallons per
minute (gpm) that the system needs to operate at
its full potential. (Example 20 sprinklers
collect 3 gpm a 60 gpm system)